If you've exported your map already, just gather up all the files and go to some file sharing website. I use Mediafire, but there's other sites such as Dropbox too. Once you've uploaded it there, just copy the link and share it on the thread you're making for the map.
In order to get screenshots up, just copy the picture link and put
around it. (Ex. [ img ] image here (without the spaces)[ /img ]). You can post it onto a photo-sharing site such as Tinypic, Imgur, Deviantart, etc. Hope this helps!