If you want babies, do nothing. The eggs may hatch in about a month if they are fertile and things go well. Do you have two or more apple snails? Mystery snails are apple snails, especially if they're laying eggs above the water line. If you just have the one snail, the eggs aren't fertile and can be scraped off. If the eggs are fertile but you don't want babies, just scrape them off. Scraping them off will usually rupture the eggs so you can't really move them elsewhere to hatch. The eggs will develop if they are out of the water but have high humidity (like the lid of an aquarium). While apple snail eggs laid in a pond almost always hatch, fewer eggs laid in an aquarium hatch.
Also, check out
http://www.applesnail.net