As Dhully says, texturing is done in the 3D application first then exported to UE4, which is why you won’t find many UE4 tutorials explaining how to do it. If you want a tutorial to help understand how to texture a model, look up tutorials on UV mapping and unwrapping for whatever 3D modeller you’re using (Blender, 3DS Max, Maya etc.). This will explain how to carve up a 3D model and apply a texture to it.