I'm going to echo Dalamb's suggestion that you post in the Strategy and Tips forum, perhaps with a new game. Take frequent screenshots, make a post describing what you're doing and why, and solicit advice. Then play a few more turns and repeat the process. You can learn a lot by doing that. You can also learn a lot by reading such threads in the archives.
I'll also suggest the
War Academy, particularly the
Introductory Courses section. I learned a lot from those articles when I started Civ IV.
To answer a few of your many questions:
1) What are catapults and trebuchets good for? When I attack a stack with them, they are the first unit pulled out of the stack to fight, they inflict seemingly no damage, and are smashed with one blow. Apparently, they can lower a city's defenses without actually moving in. What's up with that?
Siege units, i.e. cats, trebs, cannons, artillery, are probably the single most important component in an offensive army. When you approach an enemy city, there will be a "bullseye" icon. Click on this to cut the defensive bonus of the city down to--or at least close to--zero. (This bonus comes primarily from culture, but walls and the Chichen Itza wonder also contribute to it.) After that, attack with the siege units by moving onto the city. Yes, many of them will die, so make lots of them. But they damage multiple units with each attack. Once your siege has softened up the defenders, then attack with your regular units and they'll go down like dominos.
2) I am going broke. I've built markets, courthouses, and forges in cities with gold and gems (I have four, which seems like a goodly amount), plus my leader is Organized. Despite all that, I'm hemoraging money. if I don't dedicate a city to gold production, I produce negative GPT. I think it's the massive investment in defensive units that's killing me. How can Ragnar do it?
You've probably over-expanded just a bit, and a large army isn't helping either. But all is not lost. First, double-click on the gold and gem cities and make sure that those rich tiles are being worked by a citizen (a white circle will appear on tiles that are being worked). You can also add merchant specialists if you have surplus food and a market or grocer built. You'll find the specialists in the lower right corner of the screen; click the + or - button to adjust how many you have in that city.
You can also try trading away surplus resources for gold per turn. Try to get 7-10 GPT, but if you're lucky you can get as much as 15 for a luxury or health resource, or even more for a metal or horses.
Finally, there's absolutely nothing wrong with building wealth, so go ahead and dedicate a city or two to that until you're back on your feet.
3) I'm outputting bushels of culture, yet my culture war has stalled. I have a Stele (+25% culture), a Cretive leader, libraries, academies, theatres, and produced wonders and great artists. I've got the Sistine Chapel. Forget grabbing a city. Doesn't even look like I'm pushing borders back. Maybe I'm too far away. Does flipping only happen when civ's build cities right next to each other?
Extra culture buildings are a temporary solution to holding tiles. In my experience, the AI will almost always take over a tile in the long run, unless you capture or raze the city that's putting pressure on it. Distance is a factor--tiles closer to the city get more culture per turn added to them than distant ones.
4) What was that Apollistic vote thing about, and why did everybody but me vote for Saladin instead of abstaining?
The AP (and its modern cousin, the UN) is kind of complicated. Basically, the first vote, and every five or so votes thereafter, are to decide who's in charge. That sounds like the one you saw. For the AP, votes are allotted based on the population of your cities with the AP religion. AIs vote based on their diplomatic standing with the contenders.
After the first vote, the guy in charge can propose specific resolutions that can be voted up or down by a majority (or supermajority) of members. These can also be defied (automatically fail), but that carries a
penalty in your cities. Even so, it's worth doing sometimes.
5) Probably the most irritating thing: the game uses iconography as a kind of shorthand. Religions and civics pop up and offer bonuses when I have praying hands or a blue squiggly symbol in my cities. Does the Civopedia contain a key for all these icons?
Yeah there are a few:
(Well, not that last one.) Not to mention the ones that aren't supported by the forums.
You kind of learn those with time. The blue squiggly symbol stands for hinduism, and the other religions each have their own icon. There's also commerce, culture, science, and others. Explore the city screen and hover your mouse over everything, and you'll get most of them.
Finally, you didn't ask specifically, but you can counter elephants with spearmen and pikemen. Elephants count as "mounted units," so units that say "+X% against mounted unites get that bonus against them (and chariots, horse archers, knights and cavalry). You can also use your own elephants. In that case, both sides will get the bonus against mounted, so that comes out even.