The poster session mainly features work in progress. Works can be submitted to be presented as posters (which is an A0 2 column copy of the pages in the author instruction kit) instead of oral communications. For poster presentation, a Short Abstract (3-4 pages) must be submitted. Short Abstracts will be published as short papers (3 pages) in the Conference Proceedings. For creating your Short Abstract (3 page paper) go to the submissions page.
Great tips on how to create a challenging poster can be found here
You can submit a poster proposal here.