The process of mapping a 2D texture coordinate to a position on a 3d model is called uv mapping. Search for UV unwrapping or UV mapping tutorials and you should find plenty for whatever package you’re using.
Don’t give up too fast because UVs and texturing is the part of modeling that most 3D modelers dislike, especially because it is then that poor model topology is exposed.
Thanks for your support, I’m working hard and try to do things well, I work with Blender, maybe you can give me another great software that help begginners too ?
Texturing and UVs are not part of what we teach as part of Unity, as it’s really part of your modelling. That being said, we will help out as much as possible. You will, however, get much more information if you look at this issue from a modelling perspective. You should first look on the forums and chat rooms related to your favourite modelling application: Blender, Maya, Max, C4D.
Unity can support any model that is in .fbx, .dae (Collada), .3ds, .dxf and .obj formats, and Unity can also import, through conversion: Max, Maya, Blender, Cinema4D, Modo, Lightwave & Cheetah3D.
Because Blender is free, you may find it the most affordable of the options.