G Major pentatonic scale is G minus the 4th and 7th notes right? What does in second position mean?
Mark does a good job of explaining it on his site pentatonic scales
Second position means you will have your index finger ready to play notes on the second fret. In G major pentatonic that leaves you well positioned to play the root on the 3rd fret with your middle finger, the rest of the notes will fall on the fifth fret to be played with your pinky, or the 2nd fret to be played by you index.
Depending on who is teaching it, it most commonly means from a different finger on the root note, but the same sequences of notes on a different part of the fretboard. Each position has a different “shape” you follow and just uses different frets (some of them) for the same note. So for example on G Major if you fret the G on the E string (3rd fret) with your index finger or middle finger, you would fret the A on the 5th fret of the E string (for the 2) but if you fretted G with your ring or pinky finger you would get the open A by hitting the A string open and then follow the sequence from there. So first position is index on the 3rd fret, 2nd position is middle finger, 3rd position is ring and 4th position is pinky. They all have a different shape, but you can follow the scale anywhere on the fretboard (space permitting) from any finger on any of the root notes on the fretboard.
So that same shape works all up and down the fretboard for any scale?
Yes and no…you run out of space in some cases. But take c major for example. Most people play it on the 3rd fret in second position (middle finger fretting) on the A string. Then it goes 5th fret a string with pinky, 2nd fret index on D string, 3rd fret on D string with middle, 5th fret on D string with pinky etc till it gets back to C on the G string. So d the same thing with the C on the E string (8th fret) with your middle finger and do the same shape. You will play C major from that c.
I’ll add…the same “shapes” actually work for any scale (in standard tuning). So the shapeS for C Major you can do the same shape from ANY note on the fretboard and it will be the scale in that key.