A is smallest so we swap A and G
B is smallest so swap B with B (don't move)
C is smallest so swap G with C
G is smallest so swap G with H
The alternative is your approach which would force you to move a lot of the array down one place on each step.
Just so that you know though... This algorithm is trash. It is VERY slow. Bubble sort, Selection sort, and Insertion sort are the bottom of the barrel. Wait till you see quicksort and radix sort. Radix in particular just blows you away with speed but it's not as generic as quicksort.