Send data via Android Studio

I am connecting an android app using Android Studio to an arduino and I am not sure how to take the data that is inputted from the app (numbers) and send it to the arduino to make motors spin at that inputted speed. Has anyone done this or have any ideas?

Easiest is Bluetooth.

I am using Bluetooth but I don't know how to store the data so it can use it.

Storing data in the Android app is a question for the Android Studio people.