Hey RS, welcome to the club! Start with the following linked thread about structure. It's a great read and will give you a lot of ideas...

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=92463#Post92463

And, here is a thread of mine that shows off my attempts at underwater structure...

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=458150&page=2

Enjoy!

Fish on!,
Noel