left click to paint (obviously), and right click to erase, click on the arrows to change the colour and click on the other plus and minus buttons to change the size, if you can't find the right size then use the Slider bar to find the size then click load size button for it to change.
enjoy ;)
please comment if I should add anything or if there is a bug
but I may not be able to see those comments for a while but when I go online I will check