First, make sure all drivers for your entry have been assigned a valid licence and have a valid Season Pass or Event Pass. Signing up with drivers without a valid licence will get the signup rejected straightaway. Signups with drivers who don't own a valid Pass are placed on hold until they do.
If you want to, you can purchase a Team Pass to unlock additional administrative and promotional benefits. Team Passes are valid for 1 entry. Check the email you received after purchasing the pass for the transaction number. You'll need to submit that number in the signup form.
Head over to the event page and click on "Register For Event" on the right-hand side (or towards the bottom of the page if you're on mobile). You will either see a registration form there or a link to a separate signup form. Fill in the form, providing all of the required information. You can find the driver IDs on the Licence Overview page.