DETAILS OF FEATURES OF THIS CURSE PREMIUM KEY CAN BE FOUND HERE
Downloading and Installation
Login and Choose Your Startup Preferences
Start Your Epic Curse Premium Experience
Click Get Curse Premium then look for the Coupon Redemption area on the page that opens in your browser (make sure you are logged in or the coupon redemption area will not appear) and add your Curse Premium key from your "My Games" section within OnlineKeyStore
You can also reach the Coupon Redemption page from your Curse Client tool section. Just click on Tools > Options > Advanced, then click the Subscribe button (as shown here)
Your Curse account page will open in your browser where you can scroll down to the Coupon Redemption box and add the key from OnlineKeyStore.
Or from your browser, through your logged in Curse account, click on your user name > My Account. On the top right side of the "Edit My Account" page you will see a button for My Subscriptions, click on that button and then scroll to the Coupon Redemption box (see first image).
After accepting the Terms of Service (Note: #9 explains about promotional offers not requiring a credit card) your subscription will be active for 30-days. Example below: