The buttons use the label "String-Fret" (ie., 4-3 = 4th String, 3rd Fret).
Many notes can be played on multiple strings and frets. The buttons are lined up vertically above or below the notation with the choices available.
A few years ago I created the Note to Tab Tool for personal use. I wanted something that would aid in creating simple Tab riffs. This is a bare bones Web app. If you desire a full featured app that supports both notation and tab, I recommend TablEdit.
Tab files can not be saved or printed, but you can copy and paste your input into a Word Processor document. You will need the font, which I have provided the font for download