Webmail gives you the ability to easily read your e-mail through your web browser from anywhere.
POP3 stands for Post Office Protocal 3. POP3 e-mail accounts allow you to easily setup your mail program to check your e-mail.
IMAP stands for Internet Message Access Protocal. IMAP allows you to check your messages from any e-mail clients with out downloading them all first.
SMTP stands for Simple Message Transfer Protocal. SMTP allows you to send messages with out using your isp's server.