There are many house cleaners out there, and most things that remove moss/mildew/mold/algae have bleach/Clorox as the key ingredient. Wet and Forget is pretty special as it doesn't have any bleach and you don't have to rinse anything at all about 10-30 minutes later. One step really does appeal to me.
You basically dilute it with water and spray it with a pump sprayer. I chose to take a picture of this spot on my garage door as it was one of the worst hit areas around my house. When you spray it at first, it seems like it does nothing at all. But once the next rain hits (apparently wind helps as well as the rain) the magic works.
All gone, well except the dirt but it's not really a dirt cleaner in that respect.