Form autofill in my android app

Question

I wonder if anyone knows how does form autofill on android works? I mean something like this:

http://techapple.net/2014/09/5-best-autofill-apps-android-loginfill-forms-automatically-works-default-browserchrome/

"The Built-in browser that will automatically fill your login information for each of your saved LastPass sites. Lastpass also can Automatically fill forms on all sites saved in it."

Where do I start? Thanks