To enjoy your Discord role after taking a reward, you must link your Discord account to your Tipeee account. Once your Discord account is linked to your Tipeee account, the role will be automatically assigned to you the next time you log in to Discord (if needed, an invitation to the server will be generated automatically).
There are two ways to link your Discord account to your Tipeee account.
When you make a Tip associated with a reward offering a Discord role, you will find an "Associate my Discord account" button on the confirmation page of your Tip.
In case a creator has associated a Discord role to a reward you'd already taken, you can link your Discord account in your "My Account" area, under "Linked Accounts".