How to develop an accessibility feature that overlays info on the Android launcher?

I am not sure which sub-forum to post this question in Android Dev and Hacking, so I posted it here. If there is a better place to post this, please let me know.

So, I got this idea to develop an accessibility feature for Android. Sometimes people may forget what an app does on their phone. They may want to have a helpful hint displayed and/or spoken out to them when they tap an icon in their phone's launcher. For example, as in the image below, if you tap on Google Maps app, a helpful suggestion would appear as a toast saying that "Google Maps provides world maps and turn-by-turn navigation". Additionally, the user may configure to hear the hint as well. The details about how to activate the hint can be figured out but the basic idea is that the user would interact with an app icon on their homescreen or the app drawer in the launcher (either by long-pressing, tapping or some other way) and hear or see a hint about the app's action, which may be retrieved from the Google Play Store.



Now, I am fairly new to Android development and since this is quite a different thing than a standard app, I was not sure how to go about developing it.

So, specifically, what I want to know is:

1. How to identify when a user clicks on the icon of an app on the homescreen or app launcher?


2. How to make use of this event to then pull appropriate information and present it to the user?

Do I need to develop a custom launcher app to be able to identify user presses etc.? Or can I somehow retrieve this information from whatever launcher a user uses and give the hint?

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