Premium is an account boost that lasts for 30 days. You can purchase it from the Item Mall in-game for 600 points. If you use more than one Premium Coupon, the time is extended.
There are many benefits of having premium. Besides getting 30% more exp and 50% more drops, you also get unlimited Game Arena energy. That means you can do the PvP games and dungeon runs as much as you want. You will get 10 pages of Premium storage and there is no fee to place items in those pages. You will be able to access all of your storage from anywhere in the game. You won't have to find a storage NPC.
You can make up to 8 characters on your premium account (as opposed to 3 normally). You will get 10 more points for Valor quests. And everyone's favorite premium perk- you will get a daily gift every 6 hours. You do not have to stay logged in to get the gifts. The timer starts ticking as soon as you claim a box. Just log in around 6 hours after the last box. It only takes a few minutes from that time. Some of the items in the daily boxes will be account bound but others are tradable.
The first time you purchase Warpportal Energy, they have to verify your form of payment. Generally that takes less than 24 hours. You should check your spam folder if you haven't gotten a reply from support. There is a good chance the email was mis-directed as spam. That first transaction is not actually put through, it's just for the verification process.
Once you are notified that you've been approved, log in at the ROSE (or Warpportal) website and purchase the WPE you want. Then you can convert the WPE into points that you can spend in the game. You will see your points at the bottom of the Item Mall window.
The verification only happens the first time you purchase WPE. After that, you will receive the points almost instantly, as long as you are using the same form of payment.
If you have other questions, please let me know.