So what exactly is SquirrelMail? It's a web interface to email that's written in PHP4. It was designed to allow email access through your server from anywhere in the world via the Web. More information about exactly how it does this and the IMAP protocol can be found here.
If you just have a quick question, you might want to look at the FAQ.
SquirrelMail is laid out in two main sections called frames. The left frame lists the currently subscribed folders. More information about the left frame may be found under the "Folders" section of this help documentation.
On the right is where most of the action will take place. At the top of the page is a menu bar. Sign out will safely log you out of the program when you are finished. The Current Folder displays which of the folders listed in the left frame you are currently in. Right after you log in, by default your INBOX will be shown.
Under the top bar is a row of menu choices: