UART access on raspberry pi4 running on Lineage os

Hi, I am running android Lineage os on Raspberry pi 4. I am asked to develop an android app to access the UART of raspberry pi and display the status in the Android app. How to start. I am a beginner who has little experience with MIT app inventor. Pls guide Me

Welcome Allwyn.

Perhaps start here>

Thank you SteveJG.
I will try and let you know