PM stands for Private Message. To send a private message, go to the very top right and corner of the screen and have a look for where it says "Logged in as : JmwithTama" under there will "X New Messages". If you click on that it will take you to your inbox where you will be able to compose a new PM.
First you will need to introduce yourself here and make some new friends! So write a bit about yourself and see if anyone would like a new TamaTalk mate.