This took forever. I had to pull a lot of resources but I was finally able to do it in just a few simple steps.
First, go ahead and boot up Minecraft and everything.
(Not sure if you have to but just in case)
Download whatever map you want and open that file. Extract it and save it to your desktop.
Now press [windows button] + R on your keyboard.
Now, a little box should appear. It might be blank or it might now. Make sure its blank.
Type this exactly into that box:
Perfect! Now you've got the minecraft folder open.
Open the "saves" file.
Now drag your map folder that you opened up from the zip and place them into the saves folder.
Now open minecraft! Your maps should be there in single player.
Also my computer nerd boyfriend.