Hello I'm new with K2 and I need some help...

I've created my template with artisteer and I want my items' title (color, icon etc) to have the appearance that I gave to my template, but this is not happening with k2.

When I create an article everything seems ok but when I create a k2 item it's not the same.

Does anyone know what I can do?

You will need to change the css that k2 users or add a page class to your menu items and create those classes for your pages to use.
Firebug will tell you which class to change
You can put a copy of k2.css into your templates css folder and your changes will not be copied over if you update k2

And where can I find the css that k2 users because I can find only the php file

Look in components/com_k2/css directory
Watch the videos under documentation from ostraining for step by step instructions

Ok I'll try it. Thank you