Does a MCU come flashed with drivers?
The microcontroller will not come pre-flashed with Arduino firmware.
There are specific pins that are intended to be connected to an in-circuit programmer which in turn plugs into your computer through USB.
Read the datasheet/manual to find out what they are. And be very, very careful and thorough here. One mistake here can junk the entire board.
The microcontroller might come pre-loaded with a bootloader, in which case you need to find out what the startup pin configuration is, and what the protocol is, what pins are used, and what you need to do at the PC end to work with it.