How do I create opensource games?

I am planning to buy the engine. But only if I can distribute games I make without spending money. What do I do?
I know that if you sell a game, Unreal takes 5%. But what if I make a free game? What then…?

5% of nothing is nothing!!! You just have to be carefully about any money you get from advertisement ingame or on the website hosting your game. Having said that they have just changed the terms so the first $3000 every quarter has no 5% taken from it so you shouldn’t even have to worry about that anymore.