Made first sale and don't know how to get paid

go to paypal and send the buyer an invoice

Do you already have a verified PayPal account?  If you do, you can do it 2 ways, you can send him an invoice via PayPal or give him your PayPal account name and have him make a payment to that account. 

If you have not received payment, then you ought not to have to pay Audiogon, unless or until that happens. I just sold an item on Audiogon and THEY told ME not to list the item as sold until after I got paid. So perhaps you listed your item as sold before receiving payment.  Just explain to Audiogon what's going on.  Possibly you are being stiffed by the putative buyer. It happens. Obviously don't ship until you are paid in full.  Any buyer should understand that necessity.

Are you not able to have the money emailed to you?  Ship only after full payment is in your hands.  IMHO.