In no particular order.. some of the information you need to use e-mail efficiently:

E-mail addresses generally appear as UserName@emailservice.com. When someone signs up or registers for e-mail, they choose a user (or nick) name.  An e-mail address will always have the @ sign in it, followed by the name of the e-mail service provider - whether it's a POP3 or web based e-mail account.  The extension (i showed ".com") may vary.

Depending on your outgoing e-mail program, you may have the choice to send "rich text" or "plain text".  Rich text allows you formatting and other options - plain text pretty much just lets you type.  The key is...  many e-mail services only allow the receipt of plain text. If in doubt, send plain text.

Not all e-mail services freely allow attachments (AOL springs to mind).  If in doubt, ask the recipient if they can receive attachments (i.e. pictures, Word or Excel documents)

Speaking of attachments...  most e-mail services DO allow you to send/receive attachments to the mail (equivalent in a way to a snail mail "enclosure").  Just follow the directions provided by your e-mail service, and be forever aware of the size of your attachments. <see Etiquette>