How do I send a book to someone that has it on their wish list? I found someone that has a "wish" for a book I own, how am I able to see their address to mail it to them?
If you would like to offer to send someone a book, you can contact them directly to request their address - if they have Private Messages enabled you will see a "send thus-and-such a private message" link on the upper right of their BookCrossing profile page, and you can click on that to send a message. Do note that not all wishlists are up to date, and not all BCers are still active, so you may not get a response or may learn that the person no longer wants that particular book. [It doesn't hurt to include a time limit in your message - "If you'd like the book, please send me your address within X days", that kind of thing - so that if you don't hear back within that time you can offer the book elsewhere, or wild-release it, without worrying about a late response.]
You might want to browse the Random Acts of BookCrossing Kindness forum and the Bookring/ray/box forum; the former is a good place to offer books or to request trades, and the latter would be good if you have a particular book that lots of people seem to want. [If you have lots of books you'd like to send traveling, you could offer a mixed box to someone who manages an OBCZ or a Little Free Library.]
And do consider releasing a few books in the wild. Even if there isn't much BC activity near you, there may be other inactive members around who'd be delighted to find a book - or you might attract someone who's never heard of BookCrossing before!