To send someone either a note or message, put your mouse arrow over their user name and a box will pop up where you can click to send them a note or message (notes can be viewed by everyone, messages are private). You can also click on their name to go to their
homepage and at the top right corner, there are options you can click on to send a note or message.
In both of those places, you can also choose to add them as a friend. This will send them an invitation to be your friend.