Hey Hey..welcome to a real strategy game. Here are a few meta considerations:
1) Throw everything out you know about 5 & 6. IV is a unique and far more complex game
2) Strategy & Tips forum is where you need to be (requested move), but can be found here:
https://forums.civfanatics.com/forums/civ4-strategy-tips.155/
Lotsa good folks will help you out
3) My impression is that you are completely new to IV, but not sure. Regardless, I recommend you play BTS. It is the definitive version of the game. 5 & 6 are DLC based where expansions/dlc just add directly to the base game. IV is the old expansion format, where the new expansion adds a lot but you play it "standalone".
4) Install BUG/BULL mods for UI enhancements (SP mode/Custom Assets - no need to load the mod this way). Blue Marble also nice for improved graphics. All can be found here:
https://forums.civfanatics.com/threads/download-bug-and-bat-here.274636/
---this option great for forum games since folks can load your save with or without mods
5) BAT is another mod you can find there which is a standalone mod that combines BUG/BULL/graphics.
6) BUFFY is the HOF mod used for HOF games and GAmes of the Month..you can find it here - right at the top:
http://hof.civfanatics.net/civ4/mod.php
7) For really in depth advice, I recommend that you post a shadow game over in S&T with standard settings. Recommend Pangaea map with no huts and events, Noble Difficulty. Folks will give you turn by turn advice - or short turnsets - to help you get acclimated to the very important early game. Fastest way to learn outside watching videos, although IV videos are somewhat limited.
Lastly, a few very basic and general gameplay tips:
1) FOOD is king...food = production
2) Slavery is the most powerful mechanic in the game - it will take time to learn how to use it optimally
3) Most important unit in the game is the worker - it is most often your first build in the game
4) Most important building in the game is the Granary - pretty much every other building is situational.