Premium account is a kind of account limited in time with more features than the default account you created in the first place.
|no ads during game|
|Read the Forum|
|Write in the Forum|
|Profile and wall posts|
|Themes for profile and team pages|
|Form a Team|
|Chat during game|
|Vote for items|
The Gold account is a paying account for a limited time (from 3 weeks to 6 months). Once you have signed up a free account you will find on the account edit page a link to the Gold refill page.
The Gold coupon allows you to make a gift to a friend or relative. You can buy it via PayPal for 2 or 6 months. Once the payment is acknowledged you will receive a mail containing a code that you can give to the person of your choice. This code can then be entered on the Gold refill page to activate the Gold features for the account.