https://reprap.org/wiki/RAMPS_1.6
This seems to be informative if your 2.8" TFT display is a clone of the Mks TFT28:
Looks like it boils down to:
Provide it with power and connect it to the AUX1 pins.
The AUX1 pins D0 and D1 are the Arduino's RX0 and TX0 pins, so it controls your printer just like a PC would through USB.