Since we are on the C chord forms of CAGED, we'll look at playing the Major Pentatonic using the C form in the key of D.
Here again, is the setup for C Form D:
Remember, that with C form anychord, your setup is always Root, 3rd, 5th, Root and Third. Remember to always identify your roots. For C form, they are on the A string and the B string. Now having identified the roots, remember where the Thirds and Fifth fall in.
To get to the point, a major pentatonic scale needs a 1, 2, 3, 5, and 6. Using the diagram as a map, start on the fifth fret on the A string (D).
Use your pinky finger to pluck the 1, the index to play the 2, the ring to play the 3, index the 5, ring the 6, middle the 1, ring the third, and the index the 1. Play this scale slowly up and down repeating the numbers, and remember to always identify your roots (1s).