I do not have a blender instance installed right now but when you first open blender, a cube shows up. In the folowing ill type down a todo list out of memory, you should look the rest up on google/youtube yourself.
  1. import or add you mesh (tab add > some mesh or press space and enter 'add', select a mesh)
  2. select the mesh and on the right status bar click on the red-ish checkered square, its the material, add new material and name it mtl_test or something like that
  3. while still having your mesh selected choose UV unwrap > simple uv unwrap (again if you cannot find such thing, hit space and enter uv), probably you have to change from object mode to vertice-mode by pressing TAB
  4. delete everything except your mesh (lamps, camera etc)
  5. export as xmodel_export
  6. search the forum on how ti import the model and its materials in assetmanager

the above steps actually have nothing todo with call of duty, so there should alot of tutorials available