Mate, there are plenty of resources on the forum to help you with this. Not to mention, everyone's gonna have different strategies and tactics they use. The most useful thread I think that will help is a thread originally made by someone else, but one that I expanded upon:Nobodyx2 wrote:
Hello everyone, I just got an idea. How about the veterans in the game, or people who are quite experienced, write a general guide about the usage of units in the game, their combat preference, and counter units? I need feedback and also if somebody can write things down in Google Docs for each and every unit, their combat preference and counter units, also anything additional is appreciated.
https://forum.callofwar.com/index.php?thread/42842-all-ground-units-1-5-guide/ <--- My thread
https://forum.callofwar.com/index.php?thread/37847-infantry-guide-1-5/ <--- Original thread (by vietcong)
These two might be a bit outdated, but the general concept should hold and are especially helpful for beginner players IMO.
Also, go check out the community guides page here, plenty of threads to read there:
https://forum.callofwar.com/index.php?board/56-community-created-guides-videos/
BMFox also uploads CoW tutorials, tips and such on his YT channel, and altho I've never watched them, if they are as good as his old guides on the forum, then they are definitely worth checking out
(There are prolly other CoW YTbers but they aren't as prevalent as him)
Some other links you should check out:
dxcalc.com/cow <---- Battle Calculator by @DxC
https://forum.callofwar.com/index.php?thread/37805-detailed-combat-mechanics-2021/ <--- Combat mechanics by @Hornetkeeper
https://forum.callofwar.com/index.php?thread/45136-the-militia-guide/ <---- Militia guide by @K.Rokossovski
https://forum.callofwar.com/index.php?thread/39828-guide-to-espionage/ <----- Guide to espionage by @6thDragon
Plenty of resources for you and others with this same exact question to go thru. If you have any specific questions, don't hesitate to ask (unless its hospitals), either in a separate thread or right here 
(SP) Rocket Artillery, Tactical Bomber