You can sign up for your Merch Jar account at merchjar.com using one of the signup links on the page or using the link provided here in the description to find the registration page. From here enter your name, email address and choose a password. The email used for Merch Jar does not need to be the same email that you use for your Amazon advertising account.
Then click register. You've now successfully signed up for your Merch Jar account. The next step will be connecting your Amazon ad account to your Merch Jar account so you can start sinking your campaign data, which we'll cover in the next tutorial video.