AdAway blocks unwanted ads on your device. Please note that the device has to be rooted for AdAway to work properly. This means you must have administrative privileges so that it can alter your hosts file and write the ad blocking rules. Plus, it will only work on Android versions higher than 2.1.
You can only find AdAway in alternate app stores like Aptoide and if you want or need to, you can check out the source code, since the app is completely open-source. (https://github.com/AdAway)