OK. I'm new to all the online Minecraft stuff. I only play offline, as I have no internet at home, but wanted to share my maps with people.
I'm try to upload a region however on my Android phone it does nothing past pressing the upload button, and on my Mac... which I'm on now, it is greyed out in the finder window and won't let me select it.
fist, you have to pack your world, which means you have to create a (f.e.) .zip file.
you need to click "choose archive", only clicking "upload" won't be enough, as you first have to define what to upload.
after uploading your archived map, you have to upload an image and set a description.
if you want to share your map with others, check the "allow download?" option.