To track a colour, click on the color picker icon, then click on the colour you want to track in the video. Tracked objects will appear white. To stop picking, click on the first colour picker icon.
Clicking on the red button will record data for some time. Click it again to stop.
Selecting the ruler icon will set the scale. Click on the four corners of a piece of paper, then click a fifth time to set the scale.
The settings icon (the wrench) will let you tweak the settings. Colour sensitivity increase how many colours the program will track, and "Tracking Point Min Size" will determine how big an object needs to be to be tracked.