I do not understand your question.
To itch you must upload the .apk inside a zip, the person who wants to install the game (since it is not the google play store) must enable the installation of third-party applications on their mobile (many device, by default, are blocked for only allow installing applications from the google play store), download the game, unzip it and that's it.
If your question is about how to create the .apk, that is, export your game to mobiles (Exporting the game to android is not the same as uploading it to itch.io), the first thing you should say is what engine you use. But basically they all consist of you need to link the android sdk with the engine.