File uploads are possible in 4 places within OpenCollection.
file space > add files
File space is equivalent to Sakai's My Workspace. Users can upload archives of media (in ZIP, gzip or TAR format), which allows them to batch upload many files. Selecting multiple files is not allowed, however. When you select multiple files, only the last one will show up in the textbox.
registrar/lots > documents
edit > cataloguing > representations
When editing an object, users can upload media (images, audio, video) under the "representations" tab.
edit > cataloguing > docs
When editing an object, users can upload documents in the "docs" tab
edit > rights
When editing an object, you can attach files documenting licensing of rights for objects in the "rights" tab
the "rights" tab is available when editing an object; it's at the object level in other words