Well, it's pretty much what they suggested in that provided link. You're doing this on the Raspi itself, having remoted into it over
ssh, for example:
chmod +x adafruit-pitft.sh
The first command puts you in the
pi user's home directory. The second command pulls the script from the Internet. The third command marks the file so that it can be run. The fourth command will run that as the
root user (requiring the "raspberry" password for the
pi user to be promoted first).
The script will ask you some questions about the size/type of TFT screen, noting that Adafruit usually just sells the screens that are popular on the market. There are two main styles of touchscreen though: resistive and capactive. Just get that part right.
The trickiest questions they'll ask are related to what you want to show on the screen. I seem to remember that you want to mirror the console.
Here is an example collection of responses which I once did and would be similar to what you should do for the last two questions:
# 3. PiTFT 2.8" capacitive touch (240x320)
# 3. 270 degrees (landscape)
# Would you like the console to appear on the PiTFT display? [y/n] n
# Would you like the HDMI display to mirror to the PiTFT display? [y/n] y
# REBOOT NOW? [y/N] y