With the app installed on your Android handset, you are in charge of deciding which project receives your idle computing power. Current choices include Einstein@Home and FightAids@Home. The former searches for pulsars, which are spinning stars, while the latter does exactly what its name implies it does. You can also choose to donate your unused processing power to Asteroids@Home to help them study the shape and spin of asteroids.
The BOINC app (which stands for Berkeley Open Infrastructure for Network Computing) only works when you have your phone plugged in and is at least 95% charged. Data is transferred over Wi-Fi so it won't consume any of your monthly data allowance. You can find the app at the Google Play Store. And if you don't own an Android phone but would like to donate, don't panic. A version of the BOINC app for iOS devices might be on the way.
source: BOINC via PCMag