I noticed many members when submitting deals with coupon codes use descriptions like "use this coupon code" or "submit promocode at checkout".
This field is optional and if you don't have a meaningful description for it then it is better to leave it blank. The coupon code itself goes to "hot to get it" area and is already appended with text that instructs to apply it at checkout
Below is a screen shot of how it looks on the deal page:
An example of good description: "$5 off", "10% off sitewide", "free shipping", etc