I'm kicking some as*es now
But when I want to hit some1 big I keep missing it, such as: Demon/nagatar or Angel/auriel?!
Do I have to equip something special?! or what?
You will eventually need to put some points into Attack; the higher your Attack is, the less chance you have of missing it. If you hover your mouse pointer over the attack (sword) icon for that creature, it will tell you what your % chance of hitting it is.
Eventually you will be able to hit those bigger creatures, but for now just be content with going for smaller ones that you can hit 99% of the time, and your levels will gradually increase. Don't be in too much of a rush to go after the big stuff - Gothador is a game that requires patience and planning.