Apply for the AANC and people like me, mentors, will be able to explain better than in the forums.
BUT, whilst you are here, I might as well run you through it.
There are 3 types of units on different worlds. I am going to explain through the earth settings, but if you play fantasy/mars I will re-explain.
There are Infantry, which have a bonus against Vehicles. There are Vehicles that have a bonus against Tanks, and finally Tanks which have a bonus against infantry. This means that when a tank fights infantry (or inf.) it's non-infantry focused weapons fire on inf before the inf non tank weapons fire on the tanks.
For this to be explained properly, yo need to know about 3 different weapon types - concussive, beam and explosive. Concussive is anti inf, beam anti vehicle and concussive anti tank. Although concussive fights inf best, it is the 2nd best at fighting vehicles and worst at fighting tanks, and etc with the other weapons.
This means you need a mixture of all weapons to fight all unit types. Normally people build all 1 chasis as it is harder to defeat for this very reason. I suggest infantry in a 21:9 Range:Armour ratio.
Range units fire first but dont do as much damage as damage units, which fire second but pummel through armour. Armour fire last, dont do much damage, but have lots of health, which protect your range. damage is only really used early on in games
Therefore battles are won by who has the best combination of the above rules