I’m learning Unity and I browsed to http://unity3d.com/gallery/demos/demo-projects. Wich tutorial can I do first, in order of the easy to harder?
I would suggest doing the 3D Platformer Tutorial first, nice and easy to get into.
It depends on you. Browse through them. If you’re looking to learn Unity API or to navigate, you aren’t going to get far with those. Take a look at the Unity docs. There are also several tutorials on youtube.