Selling WoW Token is a two-part process--obtaining a WoW Token by paying money and then listing it on the Auction House.
Obtaining WoW Token via the In-Game Shop with Cash
Open up the In-Game Shop. The in-game shop button can be accessed in four different places:
On the bottom-left side of the character select screen
At the top of the Game Menu accessed via "Escape"
The Interface panel to the left of the Game Menu button.
The Help Window that appears when the help button is clicked on the WoW Token AH display.
Click on the "WoW Token" option on the left-hand side of the screen. You will have the option to "Buy Now" and preview the current auction value.
The WoW Token costs $20 on US servers. This price will not change over time.
Do note that this is a different item than the one you can buy on the AH--you are unable to click on this version and learn the game time by accident.
A shop confirmation window will appear showing your item, cost, and method of payment. Click the X at the top right to cancel the purchase, or Buy Now to obtain the item.
The item will be delivered directly to your inventory upon purchase, with a confirmation email sent to your Battle.net address.
Selling WoW Token on the Auction House
Visit any Auction House and click on the "Auctions" tab. Right-click on your WoW Token to have it show up under "Auction Item."
When the auction is set up, it will display the current fixed gold price and the estimated time to sell. If you are happy with the price, click the "Create Auction" button. You do not set the price, Blizzard does via their internal algorithm based off supply and demand.
A confirmation window will pop up stating the exact gold price, that your Token can't be refunded, and that the auction cannot be cancelled. If you are fine with this, click on "Create Auction."
The Auction is now created and shows up with your other auctions on the "Auction" tab.
The seller cannot specify the Buyout price and Auction Duration for the WoW Token, and buyers can only buyout WoW Token, not bid. There is no deposit.
You are sent the amount of gold promised to you in the confirmation window. If the price of the token has gone up or down since you listed it, that does not affect the amount of gold you will get.