What is this?
After you log in, you may see this spinning symbol 
in the Main Menu, on the left side of the screen. It appears next to the line which says "Check PMs" whenever you have a new PM (Personal Message) waiting to be read.
If you still see this symbol after you have read every PM, the symbol sometimes gets "stuck" on, when it should not be visible. It's a software glitch. Just send a PM to SG (the forum's owner/operator, listed first on the Member's List) and he can clear the problem for you.
If you send a PM to a member here, your message will be kept in your Outbox, until the intended receiver opens your PM. Then, your PM will be transferred automatically into your Sentbox. Each mailbox has a status bar above the list of messages in that mailbox, so you will know when any one mailbox is getting too full.