Windows: Press `Win + R`
Windows: Type `%appdata%.minecraft`
Windows: Press Enter
Mac: Open Finder
Mac: Click Go
Mac: Click Go to Folder
Mac: Type `~/Library/Application Support/minecraft`
Mac: Press Enter
Linux: Open your file manager
Linux: Go to `~/.minecraft`
Open the `saves` folder for worlds
Open the `resourcepacks` folder for resource packs
Open the `mods` folder for mods