The best Walkthrough for FRED actually comes with it. Check the help menu and do the walkthrough inside. It will answer most if not all of your FRED questions. There is some additional help available in my FAQ on the FRED page (and another walkthrough).
All this stuff is designed for FS2 but it isn't hard to adjust it to TBP.
If you like FS2 as well as TBP I strongly suggest you read up on the FRED Academy
I'm running. Sign-ups are available here
. The idea is that after going through the academy you'll be good enough that FREDding TBP missions will be easy
As for new missions for TBP there are quite a few floating about. Look for a post by Miburo and try his Tales of the EAS Janos campaign.