Combat is so frustrating

So I'm a new player and I don't want to give up on this game. I can't understand the combat. I see people in videos that 2 or three shot most of the enemies in the part of the game that I am in. For me just fighting an unarmed bandit is a frickin epic fight and they end up running away IF I'm able to knock them down or I die... every time. What am I doing wrong? I need help because I do like the game but the combat is soooooo frustrating.