How do saves work in the game? (South Park: The Stick of Truth)

I went through the beginning of the game, left Cartman's house, walked around the street, then decided to leave the game and saved accordingly. I went into the game after a while and realized that my progress remained at Cartman's house, and the loot that I found on the street appeared again ... Explain how saves work in the game, on what basis? When I click save, am I prompted to make a copy of the game's autosave? How to save progress? Just wait for the checkpoint?