When you first sign up, you'll be in your five day trial period. During this time, you'll have access to fifteen downloads per day.
Once your five day trial is over, your normal subscription will begin and you'll have access to unlimited downloads.
If you'd like access to unlimited downloads right away, you can bypass your trial from your Billing page. Just click your profile icon at the top of the screen, then Settings. On that page, you'll see your Billing tab on the left.
From your Billing tab, you'll see where you can bypass your trial.