Facebook advertising?

[AlreadyFixed.com]

FB makes you pay for each click on your ads.
You are bidding for the top spot on the page. Those who pay more/bid higher get placed higher and more often.
A Daily budget is how much you are willing to spend per day. (ie. $10 max per day @ an estimated $0.10 per click will get you 100 click throughs per day.)
If you don't pay FB will find someone who does.

You want to make revenue? Then have a way to make money when someone clicks through your ad. (ie. paid version of your app, extra credits in your app, affiliate links in your app, etc.)

If you need to market your app for free, there are other ways of doing it. Google it up.