If your Adafruit PiTFT 2.8" Touchscreen display came as a kit you will need to complete the instructions to assemble the screen. Check out the PiTFT Tutorial for more details
Download & burn the PiTFT image or use an existing Raspbian setup and install the easy-setup script. Basically, get the PiTFT setup working first!
If you want to calibrate the screen, check out the detailed calibration steps here
I found that for the most effective use of the touchscreen it was necessary to carry out the manual calibration of the touchscreen.
