I'm learning the notes on the fret board and I just wanted to ask something about the pentatonic scales you see, A minor pentatonic is A C D E G on the 5th fret, but when I play it on the 2nd fret its G A C D E, can someone tell me what's the theory behind this? Thank you guys
It's the same scale, you just start on a different note. For example if you start on the 8th fret, you will play the notes
C, D, E, G, A. It's all the same scale just where you start is different and there are many places you can play it on the neck of your guitar.
This picture shows everywhere that you can play the A minor pentatonic scale. The red dots are the root note of the scale the A in this case.
Once you remember the patterns you can easily shift it to any key. Just find the root that you want and the scale falls into place.
I believe understanding this would be much easier if we differentiated between patterns and shapes. The pattern of a major pentatonic scale is 22323, a minor pentatonic scale follows the pattern 32232. The numbers refer to the semi-tone distances between the notes. So the pattern for the major pentatonic A gives us the notes A B C# E F# back to A, and the pattern for the minor pentatonic scale in A results in A C D E G back to A. The respective first shapes of each pattern start with the root note on the sixth (low E) string.
Each of the five patterns would be a mode of that pentatonic scale. Adding the flat five (of your original A minor pentatonic) in each of those positions opens up new improvisational ideas too.