Post a song, or a video, or some text, fucking anything man. To share an embed code, use text post and click on the html button to post your embed code. Keep in mind it is more likely for your post to be approved if it is an embedded player, not a link.
Alternatively, Soundcloud users can either choose to submit their song here and attach a note saying you want it on the site:
Submit your dubstep
Or embed it with html. Simply use a
<a href="Soundcloud URL HERE" class="sc-player">Song Title</a>and insert your song url.