Orientation to Wikimedia Commons
Get to the website, and get logged in.
"Wikimedia Commons is a media file repository making available public domain and freely-licensed educational media content (images, sound and video clips) to everyone, in their own language. It acts as a common repository for the various projects of the Wikimedia Foundation, but you do not need to belong to one of those projects to use media hosted here. The repository is created and maintained not by paid archivists, but by volunteers." - cc by-sa Wikimedia Commons
Go to: http://commons.wikimedia.org and click on the "Upload file" link on the left side bar. If you're not already a member, quickly create a login.