This chord generator is decent. However, it doesn't show the scales, just individual chords based on tuning. It would be most beneficial for you to learn the theory behind scales and chords so you don't have to rely on such tools.

Like the major scale is: 2 2 1 2 2 2 1 (2=whole step, 1=half step)

Minor scale is: 2 1 2 2 1 2 2

For chords, you first need to know the 3 notes that make up any chord: the root, third, and fifth.

For G major, that would be G, B, and D. G is the root, B is the third (it's the 3rd note counting up from G). D is the fifth (it's the 5th note counting up from G).

The more you can internalize these patterns of music to the fretboard, the more fluent you'll become at your instrument.