Slashing units do 100% damage to infantry, 50% damage to cavs, and 25% damage to heavies. Piercing does 100% damage to cavs, 50% damage to heavies, and 25% damage to infantry. Crushing does 100% damage to heavies, 50% damage to infantry, and 25% damage to cavs. So if you were to attack a heavy unit with a ranged crushing infantry unit that does 4 damage you will do 4 damage to the heavy. However if you attack the same heavy unit with an infantry unit with a slashing weapon you would only does 25% damage of the 4 attack points so you would only do 1 damage to him.
The ratio you should use in units is a 7:3 range to armor ratio, meaning 21 range units and 9 armor units per squad of infantry. 10 range and 5 armor or 11 range 4 armor per squad of cavs, and 7 range and 3 armor per squad of heavies. You should not mix chassis in your army so only build one unit type whether it be infantry, cav, or heavy. When you build your squad all of your armor should be slashing weapon since they die last in battle, it will save you armor units. For example, a squad of anti heavy units will have 21 crushing weapon range units and 9 slashing armor units. Your range units you will want to build for what you need, if you have no specific enemy at the moment try and keep a balance between your weapon types. If you have any other questions feel free to ask me or you can apply for a mentor viewtopic.php?f=401&t=1036