Carefully stick tape down on the bag where you DON'T want the paint to be. You can make the stripes even but I decided rather than stress about making them all the same I did more of a gradual design with the larger stripes at the bottom
Wrap the tape around the corner so you won't have to worry about getting too much paint on the sides
Carefully paint on the red paint being careful on the sides and top
I only needed one coat, when it's dry, in about an hour's time, carefully rip off the masking tape
And enjoy your new red striped bag!