say my city is being attacked by land units and i have 1 unit to defend with, do i garrison it in the city and what good does it do being there, it doesnt seem to attack anything

what good are research agreements and why does the computer always want to make them with me

why is expanding with new cities detrimental when a settler only takes 1 or 2 turns to build and theres space open

no idea how to do anything with city states, they are basically a road block to expansion and nothing else until they decide to declare war on me for no reason

if they attack a garrisoned city the attacker will take more damage from the attack (takes damage from both), your unit will not be damaged. there are also social policies that benefit from garrisoned units, either a defensive bonus or a happiness bonus or even a free maintenance unit.

research agreements, after the 30 turns, provide a science bonus to both parties. so basically you are paying gold for a future one-time science buff. you are also giving it to your trade partner too though.

population size/number of cities hurts happiness, and once unhappiness production/gold/growth slows/stops etc. so you cant out expand your ability to keep them happy. social policies provide happiness bonuses, science unlocks happiness buildings, luxury resources provide happiness. city-states are a huge way to get "free" happiness. once you make friends/allies they start gifting you their resources/units/food/culture depending on their type. its a gold investment but you should be able to afford it at some point in the game.

also, trade with the computer your excess resources, this will help the happiness too.

they declare war on whomever their ally declares war on. it happens and cant be avoided, its tough to buyout all the civstates, but you should absolutely be able to get at least one in your pocket, they they will fight for you if you go to war.

9 hour civ game, finish spaceship, aaaaaaaaaaaaand its gone, exit to main menu

just like real life science victories on a smaller scale