In addition to My Page, you have an inbox. Have a look at it, it is on the right handside, top box under your name.
You can send private messages (emails). Very handy when you want to communicate your phone number or private email address, it is a safe way to do so.
To send a message to another member:
-> Go on his/her page (click on the icon "members" above and find the person you want to send your message to).
-> Click on "send a message" under their photo.
-> Compose and send.