This is (to be) an animation of the partition algorithm found in CLR's Algorithms book.
PSEUDOCODE FOR PARTITION (taken from CLR)
Goal: Partition section of array A from A[p] to A[r], inclusive.
Set Pivot to value at A[r]
Set low numbers boundary i to p-1
Set high numbers boundary j to p-1
if A[j] < Pivot
then swap values in A[++i] and A[j]
swap values in A[++i] and A[r]