Buy tickets to see a game at Stade du 4-Aout. If there's nothing happening while you're in town, you might like to check if they give a guided tour of the facilities.
You'll be spoiled for sightseeing choice in Ouagadougou. Stade du 4-Aout is a good place to start here, but there are plenty of other fine places to check out. Ouagadougou Cathedral, University of Ouagadougou, and Place des Cineastes are not far from the sporting facility and and will cap off your day nicely.