Noob with a Xbox Controller...

Assassins creed seems pretty neat for a started to get used to a controller
or any open world games like GTA

My switch from KBM to GP was quite easy, but I have luck of quickly adapting.
I would suggest to go with a racing or driving game. Just not an arcade. Something that at least hints you are driving an actual car. Racing games are great to hone your precision, but not as demanding as shooters.

thank you all for your suggestions,im glad some ppl havent lost theyr "helping hand"...or smth like that...u get it xD

I have bought one mainly for fighting games, that fits perfecyly on a controller. So Try something like Street Fighter. However, the firsts games that I played full on a controller are Mirror's Edge and Renegade Ops.

racing games, BoI, super meat boy

Batman, Assassin's Creed, Sleeping Dogs,Fifa

any LEGO or Racing game.

Ys Origin or Ys: Oath in Felghana. I tried to play Ys Origin with a mouse and keyboard, and it was pretty much an exercise in frustration even on very easy. The multiple skill levels will help since you can start on a lower one and move up as you get more used to it.

I'd not recommend playing on nightmare or hard while still getting used to a controller, because that does require more precision, but normal and lower don't need it so much. Also, change the defaults because a few defaults suck. Mostly you want to move the menu, walk and magic/skill ones. Skills are great on the right bumper, walk on right stick, and put menu on start or back.

You might prefer Oath in Felghana to start with. Try it on easy so you can enable no fall mode (that enables it so that if you fall down in a spot that leads to another area, it takes you to a spot in the same area instead). There's a few spots where you likely will appreciate that as you get used to the precision with a controller and you'll still have to learn how to do the jumps, but won't have to deal with the frustration of falling to another area and backtracking until you got it down. But the jumps and attacking are actually much easier on a controller.