I have learned a few of the major pentatonic scales but I don't get what makes them different. I mean I can obviously hear the difference but like what is the theory behind it? How can I figure out the minor pentatonic scales from knowing the major ones? I don't know what any of the notes are, so if you can please explain it like with the string and the fret that I have to play.
You differentiate between scales by the notes they contain and the intervals between those notes. Frets and strings are meaningless for this, if you don't know the notes then you need to learn them,
Actually called Mark!

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It has to do with degrees.

Pretty much, say we're in the key of C. The key will tell you what notes you're allowed to use, and C is easy because there are no sharps (#) and flats (b). Each note, starting with C, is numbered. This numbered note is a degree.

1st degree: C
2nd: D
3: E
4: F
5: G
6: A
7: B

And at that point you've used up all the letters of the musical alphabet.
If you play these notes on your guitar, you may notice a pattern to this which will help dechiper the notes in the key. It's called tone tone semitone tone tone tone semitone.
Sounds odd? yeah, but stick with me.
Pretty much, a tone is two frets up (C to D).
A semitone is one fret up (C to C#).
I'm sure you're dying for a tab, so here ya go:


You can count the frets as you go up the neck, and it fits the pattern! two frets, two frets, one fret, two frets, two frets, two frets, one fret. Of course it's silly to play a scale like that so you probably play it something like this:


As you probably have realized by now, if you want to know the answer to your question, you need to learn what fret equals what note. An easy way to do it goes back to lesson number one: tuning your guitar. You've maybe learned by phrases like "Edgar Ate Dynamite Good Bye Edgar" That the open strings are E, A, D, G, B, and e. And you know that to tune, you play the 5th fret and then an open string. Now, remembering that a semitone is one fret up, you can count up the notes. Starting at low E:
0 fret: E
1 fret: F
2 fret: F#
3 fret: G
4 fret: G#
5 fret: A

and of course 0 fret on the A string is A. You can connect the dots from here. if 0 fret on the A string is A, then the 1 fret on the A string is A#, or Bb. And if 5 fret on the E string is A, then the 6 fret is also A# or Bb.

If the b is confusing you, a semitone up from A is A#, but a semitone down from B is Bb, which is the same as A#, it's the middle ground. It's also important to note that there is no space in between B and C or E and F. There is no B#/Cb or E#/Fb.

Ok with all that in mind, you should be able to locate notes on the fretboard. Now the next part is pretty simple. The minor (pentatonic) scale is the 6th Degree.
So after counting the notes (or referring to the top of this post!), you'll find that the 6th degree is A. And the A starts at the 5th fret on the E string, so if a song was in the key of C, you'd play this scale:


This is called the Am Pentatonic, and it's a pretty popular scale.

Ok now lets go back to the first degree, C. The first degree is called the tonic.
And it's also the root note of the major scale. The root note is the starting point in a scale, for example in the Am Pentatonic scale above, the first note is the 5th fret (A) therefore the A is the root in that scale. This is what makes major scales differ from each other. The root notes are different, which means they are played in a different key. For example, if a major scale starts on the 3rd fret on the E string, it is in the key of G. If it starts on the 5th fret on the E string it is in the key of A.

Now you might be confused. But with that pentatonic, you said we were in the key of C, but that scale starts on an A! Well, back to the degrees. Degrees pretty much tell you the notes in a key, but each note is also a root note for its very own scale! This is called modes, and opens up a world of fancy names such as mixolydian and dorian and stuff like that, but I'll keep it simple. Major is the 1st degree, and Minor is the 6th.

Ok that was a really long post, and a little unorganized I'm sure, but I hope you followed along just fine and have a stronger grasp on scales now! I tried my best to keep it condensed but still specific. This is like three different lessons in one! Let me know if it's still unclear.