purgatory is the “middle” of both heaven and hell. It is commonly believed by Catholics. If you end up in purgatory, you will make up for all the sins you have done in your life. It is the stop you are at before heaven. Anyone in purgatory is on the path to heaven, but they need to be fully “cleaned” and pure again before entering the sacred place. The sale of indulgences was a scheme made by unlawful religious teachers. They would physically sell things that make ones punishment less harsh for the sins someone did. This was completely awful as these people who sold the indulgences didn’t have a say wether their punishment would be harsh or not. It was ultimately up to god. They did this just to make money for themselves or the church.