Pressing the Calibrate... button begins a new calibration. The calibration window covers the entire desktop, or in DualView modes the part of the desktop shown by the monitor. Press Escape to stop calibrating at any time.
Press the touchscreen with a fine pointed object, and move it to the cross shown in the window. It is important to start somewhere other than position where the cross is shown, and then gradually move to the exact position of the cross rather than directly pressing on it. This helps to prevent against wrong points being registered during the calibration. You can see the current location of the pressed point (in device coordinates) in the upper left corner of the window.
Once you are touching directly over the cross, press any key on the keyboard. This will move onto the next cross.
Repeat this for all of the crosses. It may take several attempts to get the best calibration.