Here is the G major scale. As you can see the first note played is a G. This is known as the root note. This same rule can be applied to all keys. I have also included the Major Pentatonic scale. This scale is very similar to the major scale. The only difference being the 4th and the 7th note are not played. The scale consists of 5 notes which is why it's called the pentatonic scale.

G major scale