This handbook, once read in full, should answer all questions you might have about Enigmail and give you a thorough understanding of it. You can always find the most up-to-date information (and Enigmail executable) directly on the Enigmail official web site:
Should you experience problems or want to ask further questions, you can obtain support (provided by volunteers) from several places: there is a Forum, a mailing list, and a newsgroup dedicated to Enigmail. For information about how to access them, visit
http://enigmail.mozdev.org/support
If your question is not strictly related to Enigmail but rather to broad OpenPGP topics (e.g. signing, encryption, key management, trust...), you may also address yourself to the GnuPG resources. GnuPG documentation and support is available at