It seems, RD-BH, that you are interested in drawing some sort of conclusions from what you are being told. So, I'm going to skip directly to some conclusions for you.
Do what I suggest, even if you do not understand why. Try out all of my suggestions at once in another practice game. You will see a TREMENDOUS difference compared to the game that we see in your screenshots.
A) Do you see those mined Silver Resource squares in your images, the ones with 1 Food, 2 Hammers, and 5 Commerce each? Be sure that those squares are worked! One Priest Specialist will net you far less benefit than one of those Silver Resources squares.
In fact, if you are using Slavery to Whip production in that city with 2 Deer Resources and 2 Silver Resources, I would ask that once that city grows to size 4 population, never whip the population to a value below 4 population and thus never stop working those 2 Deer Resources and 2 Silver Resources with your minimum population of 4 population. So, if you need to whip a unit that requires the sacrifice of 1 person to whip, do so when the city's population is 5 population or higher. If you need to whip a building that requires the sacrifice of 2 people to whip, do so when the city's population is 6 population or higher.
For a beginner player, I would suggest that you ALWAYS make an effort to work any mined Silver Resource square, as long as you are also working enough other Food-producing squares for your city's population to still be growing.
I would give you the same suggestion for any mined Gold Resource square or any mined Gem Resource square: be sure to work those squares at all times, as long as you have enough Food from other squares being worked for your city to still grow.
B) If your city is working a Forested square that is next to a river, then you need to get a Worker to that square as soon as possible. Have that Worker either Irrigate (i.e. put a Farm on) that square OR have that worker put a Cottage on that square. Compared to leaving the Forest there, choosing either one of those options is better.
If you remove the Forest from the square that is next to a River, you will gain 1 additional Commerce by working that square than you would by working that square when the Forest is there. You will ALSO get the benefit of more Food (from the Irrigated Farm) or of more Commerce (from the Cottage) whenever your city is working that square.
I notice that in your screenshots, you are researching Math. DO NOT WAIT until you have Researched Math to implement this Forest-clearing suggestion. Start Irrigating or putting Cottages on the riverside squares earlier in the game, as soon as you have researched Bronze Working plus the relevant technology of Agriculture (for Irrigated Farms) or Pottery (for Cottages).
The reason why you do not want to wait is that you want any city working those squares to get one extra Commerce per turn as soon as possible. In so doing, you will be able to research Math even faster, meaning that you will get the additional Hammers from chopping Forests MUCH SOONER in your game, which will more than make up for "missing out" on some Hammers by chopping a Forest when you do not know the Math tech.
Similarly, if the square beside a river that has a Forest on it is a Hill square, then put a Mine on that square. You can do so immediately after researching the Bronze Working tech, without requiring you to research any additional techs.
C) In an Immortal level game, do not build The Pyramids. In fact, don't build any World Wonders except for one World Wonder. Pick the World Wonder that you want to build before you start the game. Write that Wonder down on a piece of paper. Build that World Wonder and only build that World Wonder. Don't build any others. If you do not see a Stone Resource in the game's starting screenshot, then you should not have written The Pyramids on your piece of paper--if you did write it down, scratch it out and pick a different World Wonder.
If an AI beats you to building that World Wonder, don't build any other World Wonders. Yes, a non-beginner player might be able to ignore this advice, but for a beginner player, this advice is going to greatly improve your gameplay.
Certainly, you can and should build many National Wonders. It is the number of World Wonders that you should limit.
D) If you do not own The Pyramids, then I recommend that you limit the number of cities using Priest Specialists to TWO CITIES. Other cities should be working Resource squares (for example, Deer), mined Hill squares, Cottaged squares, or Irrigated Farm squares.
If you DO own The Pyramids AND if you switch your Civics to use the Representation Civic, THEN and ONLY THEN should you consider using Priest Specialists in more than two cities.
Why do so in only two cities? Well, the biggest benefit from Priest Specialists is going to be netting you Great Prophets as your generated Great People. The biggest cost is the loss of opportunity to make more than 1 Hammer and 1 Wealth for each citizen in your cities.
If you have two cities producing Great People, you will make relatively efficient use of your Great People Points.
If you have 3 or more cities making Great People by employing Priest Specialists, you will only be marginally getting Great Prophets faster. However, you will be absolutely killing your opportunity to make more Production (from Hammers), more Research (from Commerce), and more Wealth (from Commerce). The trade-off of losing out on that Production, Research, and Wealth in order to get then next Great Prophet a tiny bit faster is NOT WORTH DOING!
E) Build Roads. Not just randomly-built Roads. Not Roads on every square in your empire. Focus the placement of Roads so that your cities are connected to each other. Do so early in the game. As soon as you build a new city, do your best to make sure that Roads are connecting it to at least one other of your cities as soon as possible.
In so doing, you will be creating Trade Routes between your cities. Your screenshots show a complete lack of Trade Routes.
Not having Trade Routes is one of the main reasons why your economy is crashing on you so quickly. Think of Trade Routes as FREE Commerce. So, think of them as FREE Research and FREE Wealth.
All you need to do is connect your cities up by Roads to each other and your empire will see a HUGE relative gain in the amount of Commerce that you are making compared to what we see in your screenshots.
There are other ways to connect Trade Routes than by Roads, such as by using Rivers and by building cities next to Coast squares, but forget about that fact and simply BE SURE TO CONNECT EVERY ONE OF YOUR CITIES TO AT LEAST ONE OTHER OF YOUR CITIES BY ROADS!
If there is a path from your capital city to each of your cities by Roads, then you can get slightly more benefit from Trade Routes when your cities grow in size, but minimally have each city connected by Roads to at least one other city in order to gain the biggest relative benefit.
F) Build a Road on each of your Resource squares and make sure that said Road is connected to at least one of your cities by Roads. I notice that neither of your Silver Resources have Roads on them. You are missing out on potential FREE Happiness in each city. One more Happiness would mean having 1 less Warrior per city when using the Hereditary Rule Civic, which it appears that you are using. When you have that many military units, each military unit could be costing you 1 more Wealth per turn.
So, simply by connecting your Silver Resource to your cities by a Road connection, you willl be able to reduce your Wealth expenses, meaning that you can put that unspent Wealth to better uses.
If you connect all of your Resources in this way, you may eventually be able to trade some of your duplicate Resources to some of the AI, in exchange for their Resources or for a payment of Wealth per Turn (aka Gold per Turn).
G) Be careful when you switch around the squares that a city is working, as well as which Speciliasts the city is employing. Notice that in some of your screenshots, you have actually hired the Citizen Specalists, the dudes in grey with the hats on their heads, located just beneath your Priest Specialists. You do not want to hire Citizen Specialists. Instead, make sure that you switch those Citizen Specialists to either be a different kind of Specliast (such as a Priest Specialist) or to be working one of your city's squares, such as a Silver Resource.
commerce and 
wealth are not the same thing.
)
(125 if each of your cities has a Library). But you are losing 30 
).
directly to 
