First, you need to get set up as a regular user. For details, see the Quick Start guide.

Go to the Prices page and buy a bundle of activation codes. The list of activation codes will appear in My Account->Reselling.

Find a customer and get paid. Once the payment is received, go to My Account->Reselling, click the envelope next to the activation code you are selling, enter the username of the buyer, and submit the form.