Actions are the key elements that make up the client. Essentially the software has an idea about what the local and remote storage locations contain and then makes decisions about which files should be uploaded / downloaded or merged (in the case of a clash). Currently merging is not yet supported however will become so using a plugin based system.
Actions are not generated for Files or projects that are marked as 'ignore'. These actions are
A view into the local filesystem.
A view at the remote filesystem - greater control is available here showing server details and remote path. The capacity of the remote filesystem is also shown to keep track of how much disk has been used.