If you have arrived there you must have encountered (and won) other fights already. The principle is the same just with more people.Didn't help me. I don't understand this game
The most important thing is to get the sequence of actions right. Namely: lacerate must always be first in a cycle because it makes the enemy bleed (lose hit points per turn); defend must always be last because every third enemy hit is more damaging; recover and tag team help increasing the base damage you inflict.
If you still have difficulties you need to craft rations, med kits and ammos to buff your defend, recover and firearms abilities.
If you have still issues, maybe your basic stats are low. How much is your fitness and your will? the first affects your basic damage and the second the number of actions per day (which doubles as your hit points)