What is Flashing a device and how to do it?

Hello. Thank you for your time and attention.
I think I have a malware. let me count the ways:
Battery drains rapidly.
High network usage.
If not in Airplane mode, battery drains in hours
phone battery will die when plugged in and sleeping.
Cannot access google search.
Cannot access Chrome, maps, you tube, play store, Malwarebytes app, flashlight, or any saved website.
52% RAM used and zero running apps.
I am restricted from viewing the mobile data usage of the pre-installed flashlight app as well as most every other app on my device.