"Collections" are specific groups of images curated and chosen by FAA staff. You won't show up in those unless one of your images has been picked, and that happens at owner/staff discretion.
The regular search returns are based on a number of factors, many of which are not known to the users of the site. But if you are new, try to make sure your keywords are complete and detailed and accurate. Try to be specific, and think in terms of what people would ask for if they were looking for your images.
Most importantly, don't rely on internal search to make sales. Use email and social media to send potential customers to your portfolio here. You'll be far more successful if you consider FAA to be a storefront for you, and you do your own marketing. There are a lot of discussions about marketing and getting started, just search the discussions.
Best of luck to you!
