Hello I just got this game and watch some videos but i never find anything about monsters so I was wondering if there can be more then one monster in a space? And if so how will evade or fight work? Do i fight one at a time or both?

Yes, you can have more than one monster in a given space. In this case, you deal with the monsters in the order of your choosing, one at a time. You can select which ones to evade and which ones to fight.