To setup your billing, just go to the top-right menu (under your avatar) and click on My Billing.
If you don’t know yet which is best Plan for you, click here to get more info.
Make sure you add your credit card in the 'Payment Method' tab, and select the Plan.
You can increase the limit of the Services to be used in each Profile (initially you will receive 1 Profile).
Also, you can select a support Plan and Add-ons.