Minecraft is quite unique in the fact that you can download and play any version that has officially released since Alpha. There are countless versions, but of those, only 5 are truly game changing. There's 1.0, the official release of the game. 1.7, which added many new biomes, structures, and more. 1.9, which changed how combat worked and added in new equipment. 1.13, which added ocean structures and a new swimming mechanic. 1.16, completely revitalized the nether. And 1.18/1.19, which increased the world height, revamped cave and mountain generation, and many more.