Hi, Lighter - welcome to Showbie!
Start by opening a PDF or image file in Showbie. Tapping on the highlighter icon selects it, but tapping a second time will open the colour palette. Here you can select other highlighter colours and sizes to use. Highlight all of the important parts of your file and tap on Done to save.
Do you know that you can also draw straight lines? You can straighten a line you've drawn with the highlighter tool by holding for a few seconds. You can even connect the lines to create shapes!