Asset creation is not simple and all of the possible programs require a very considerable effort to master. However, a great deal of satisfaction can be obtained.from the process. Even if you don't persist to the point of making assets which are suitable for release, you will gain a good insight into the techniques involved and how much work and skill the content creators put in.
There's a lot of good information in the Asset Creation section of the Trainz wikibook.
yes, i believe two people have. you click new asset in the file menu in cmp. this will take you into ccp. if you need a tutorial, i can point to several that will help in this process