Did you read the wiki on how to do maps for MW:LL?
Yes?
And You still hit the wall?
Tell us what the problem is here, and we try our best to get you through to the finished map (and update the guides on the wiki alongside too, hopefully)
The same applies if You happen to are already familiar to SandBox2 editor, but want to add new art to the map.
Please be polite, and we will try out best to to help.