Visit the Applause Store website. Click on the text "Register" at the very top of the page. To be placed on the reserve list for tickets, you will need to take out a free membership with this website.
Fill out the registration details required. Once this form is submitted, Applause Store will send an email to the account with which you just registered.
Open the e-mail, and click on the link supplied. Enter the verification code included in the e-mail to complete the registration process.
Scroll down to find the listing for "Top Gear" in the purple list at the top right of your screen, and click on it. This will take you to a page listing all shows for which tickets are available. Scroll down to the Top Gear listing, and click on the "Reserve List" text.
Click on the gray "Submit to Reserve List" button in the middle column of the page.