The AADSAS number doesn't mean that your application was sent to schools, but it does mean that AADSAS has received your application.
They will send you an acknowledgement receipt form in the mail, which also lists your AADSAS number.
The number is the order in which your application was received/is being processed.
Last year we had to print out a form, fill out our return address, and send it via snail mail to AADSAS. They then stamped our number on it and mailed it back to us when they received our application. Maybe things have changed this year and you no longer need to mail the form if you want a acknowledgement receipt.