How to make slits in a skirt
A. Using a small pair of sharp scissors or a seam ripper, remove the seam stitching in
the hem of at the bottom of the skirt where it meets the seams for the side of the skirt. Don't undo too much - only enough to get to the end of the side seam.
B. Gently pull away the bottom hem to get to the side seam. Remove the side seam stitches with your scissors. This is where you choose how high the slits go - only remove the stitches that far.
C. Now turn the skirt inside out and snip the spare seam material at the top of your open seam. Place the sides of the seam flat and then iron them.
D. Finally fold back the bottom hem in place and sew along the flaps on the sides of the slit you have made (from bottom to top). Tie the thread at each end to prevent unravelling.