The main strategy of the first few rounds is put Argo in places where units can't get by him and let him tank all the hits . Watch out for vise though because she does extra damage to armored on the last mapSure im an old hand at these.
Units with melee weapons: axes,swords lances. These are the units you cam risk taking hits.
Units with ranged weapons like magic and bows, generally are weaker but dont always get counterattack and counter certain enemies.
Next is unit types. The main character is an armored unit which means he's good at taking physical damage, but is slow and weak to magic. The first girl you get is a healer. She's squishy but does magic damage and can heal your other injured units. Fez actually has a further breakdown of things in the game, but you need to get through the prolonged first