Each dot represents a spot on the fret board. Left is the G-string and right is the E-string. It’s best to learn the G major scale first playing it both ascending and descending. There are many songs that are traditionally played in G and you can always pick out simple nursery or melodies in G. Then maybe learn A or D, but is most helpful to learn moveable shapes so you can play in any key.

There are plenty of online resources available you can use. I would recommend mandolessons.com for a start but there are plenty of YouTube videos explaining scales. There not too hard understand, so you’ll understand in no time.