How do I view the monthly free stuff I'm supposed to be getting for my subscription?

From the DDB article on May subscriber perks:

If you are not subscribed, you can see this month's perks on our subscription page. If you're a current subscriber, you'll receive a monthly email that details the perks.

Once you receive your perks, you can find character sheet backgrounds and character portrait frames on your character sheets. Simply go to My Characters and click "View" on one of your characters. From there, click on your character name or "Manage" and then "Change Sheet Appearance" to access the backdrop, frame, and theme customization menus.

Your digital dice collection can be found on the My Dice page.

If you're a current subscriber but can't access this month's perks, go into your account settings and click "Sync My Entitlements."

You're the bomb.