How can I screen mirror my Android to my tv I use a onn tv and a Motorola fone and my screen cast doesn't want to work
Are you trying to cast or mirror? Those are different things.
If you're looking to mirror, try this page: https://support.roku.com/article/208754928
If you're looking to cast, try this page: https://support.roku.com/article/360002990094
Your ONN TV may be missing the screen mirroring functionality.
There is currently a bug impacting some ONN Roku TV models where the screen mirroring (and potentially other WiFi Direct based functionality) is missing
Check to see if Settings/System/Screen mirroring exists in the UI menu - if it doesnt your ONN TV is also currently suffering this bug, and you should report it to Roku: