People create some truly amazing worlds in Minecraft- from fantastical architecture, to mechanisms, to complete rapid transit systems.
And sometimes the creators make their worlds available to download for your enjoyment. Then you can explore the world freely, modify it, and look inside to see how it was built.
Unfortunately it’s often left as assumed knowledge as to how to add these downloaded files to your copy of Minecraft.
I’ve done some research and these are the best guides I’ve found so far. Let me know if you find a better set of instructions, or if you need more help. I can write further instructions or create a tutorial video.
Desktop Computers (Windows, Mac, Linux)
iOS and Android (Minecraft PE)
Both platforms use the same file format for worlds. This means you can move worlds between these two platforms, so long as you’re using the same version of the game on both.
For iOS There are several articles that make reference to tools such as iExplorer. However you can also use iTunes directly.
I found this instructables explains the process clearly, for both iOS and Android.
Game Consoles (XBox, PS4, Etc)
Unfortunately there is no easy way to copy Minecraft worlds to or from these platforms. They’re very closed in nature and don’t encourage any end-user modifications. There may be means to do it but my brief research lead to guides requiring hacking and modification tools. Their use is most likely in breach of your end user agreements. I’ll leave figuring this out to an exercise for you, dear reader (but I wish you luck!)