Google is your friend: Be nice and visit him often. He can answer questions a lot more quickly than posting them here...
Less than a minute with google gave me this:
How to Write HTML/CSS Faster with Emmet Cheat-Codes[
^] When there, use CTRL+F to search for $ and it explains how to start with a specific number.
The search term I used was trivial: "Using $ in HTML emmet", the first part copied from your subject line, with the word "emmet" tagged on the end.
In future, please try to do at least basic research yourself, and not waste your time or ours - you could have found this over two hours ago if you had ...