Well.
You download winrar, or 7Zip.
Then you find your start button and type in %appdata%
Then find your .minecraft. Navigate to the saves folder inside. Then find the map you want to upload.
Drag the map onto your desktop.
Click, and right click it, add it to (WorldName).rar
This is the ZIP folder you will upload to either MediaFire, or dropbox.
After you upload it to one of those sites, you find out its download URL, and paste it into the Download URL section of the map editing.
That's how you do it on PC.