I have a model made in blender. I’ve got the texture mesh from 3d MAX. The model is currently .obj and texture is .bmp.
How do i apply texture on a model to show up in editor?
You should read the documentation on materials before going any further. Just like rendering in Blender, textures are not applied directly but are used as part of a material, allowing you to configure things like surface roughness and normals in addition to the base colour. Also UE4 can accept OBJ just fine but prefers FBX, which has more features (OBJ, for example, doesn’t support animations but FBX does).
so i read this
Where i might paint things black and white?
As the documentation you linked says, literally any image editing package will do: just draw in white and black.