Not Sure Where to Start: Custom Android App separate from Particle App

Hi there!
I’m trying to figure out how to get started on a new project for me … the hardware side I think I have … but not yet sure about the interface yet.
I’d like to be able to control my Particle with an Android App that’s separate from the Particle App. That is to say, I’m trying to teach myself how to create a basic Android App and would like to be able to control my Particle device from that without needing to open up the Particle App to do so.

Where would I get started finding tutorials/information for that?

Thank you!