You create a .zip file, although you copy the map and then you zip it

i do it this way
1. save world
2. go to .minecraft file (in %appdata%)
3. click on saves
4.right click on your world you want
5. click on the zip thing
6. wait for it to be done being a .zip file
7.move the zip file to any file you're comfortable with, i choose downloads.
8. if you have a mediafire account, good. if not, create one.
9.go to mediafire.com
10.press upload
11.click on the + sign
12. select the world (.zip file one)
13. wait for it to upload
14.copy link to the download
15.upload the world on planet minecraft with some screenshots
16.DONE!!!

First, go to the bottom of the world options and press export. Then you wait for the export to finish. Once you're finished with that, go to the map uploader on PMC and press upload file. Make sure the file isn't too big! Once you press upload file, find your MC world and you'll be set!

Is your map file .zip, .schematic, .mcworld, .mctemplate, .schem or .nbt?

Also is it bigger than 15MB?