How to create texture for OBJ files

Hello everyone.
I’m looking for adding a tree on my scene.
I have a .OBJ file that I converted into a j3o and imported on my scene. It works well but that tree is not textured.
I’d like to know how to do that.
The FAQ says “Create a PNG texture file” but how am I supposed to do that ? (I work with photoshop).

Thank’s a lot!

The UV map is stored in the mesh so you can reapply the texture by selecting a geometry in the SDK SceneComposer and selecting “create j3m”, which will create a j3m material file where you can assign the texture. All this after importing the model to j3o