Ev
You are assigned a Secret Sister (SS) and you send to her without telling her who you are. Most of us use our SS's own address as a return address on the envelope or package so she doesn't know where we live. Than when she receives the mailing, she comes onto the board and thanks you. Because she doesn't have any other way of saying thank you.
Now, how you get yours. Someone has been assigned your name and is doing the same thing for you that I just mentioned above. Sometimes SS use pretend names to sign the mailings just for the sake of making it more personal. I know, I've read some really cute ones on here this time around. I like the idea.
If I haven't explained it clearly enough, I just know that Kay, Linda, Marcia or another sister will be on shortly and do a better job. Just keep asking questions and we'll just keep answering. 
nancy