Private Messages (or PMs) are, as the name suggests, messages between members that are private and cannot be seen by anyone else. They are sent between two members and written like a normal post.
How do I send a PM?
You can send a Private Message by viewing the profile of the person you would like to send a PM to, and clicking on the link that says "send a private message to (member)". Alternatively, you can send a PM by pressing the "reply" button on the bottom-right corner of a PM that you have received.
What are PM folders, and how do I use them?
You can make custom folders for your Private Messages to go in, by clicking on "Edit Folders" under the "Private Messages" section of the control panel on the left. To put messages into a folder, click the checkbox of all the messages you'd like to move, and select "Move to folder..." from the drop-down list in the bottom-right corner. You can then choose which folder you would like to put the messages into.