Category ads is an add-on product that you can buy to make sure that your ad will be shown on the first page of your category:
(Categories are: Girls, Boys, TV-TS, Couples, Clubs and so on)
(image is from category girls)
On your ad, click payment, buy some Category days, then go to travelplan and add them to the days you want to be on the Category ads page.
You can see which position you can get if you hold your mouse over the check box [x]
See image below.
If you get position number 3 you will stay number 3 that day unless someone in front of you drops off, when you will get an even better position. You cannot get a worse position and you will always stay number 3 or better if you got 3rd place when you booked your Category ad.
So remember, book many days, book now, and the sooner you book, the better the place you will get!
Only 6 Category ads are available in each category.