Adding a show is really easy in ted. Click the "Add show" button (), or choose file -> new from the menu.
If you check this box, ted will only download torrents for episodes that are published in HD quality (720p). You can later change this preference in the edit show dialog.
When your show is not listed in ted, you can add it yourself by clicking the Add custom show button. You will be presented with the dialog that is also used to edit detailed show information, that you can use to enter the details of your custom show.
So now you've added your first show. ted will search for new episodes every x seconds (depends on your configuration).
When ted finds a new episode, it will save the torrent and will try to open it in your torrent client, if you checked that box in the preferences. ted will increase the episode number and go search for the next episode.
If opening of a torrent does not work on your machine you need a client that checks a certain directory for new torrents. Azureus does that for instance.
Any errors that ted encountered are logged in the log, see edit -> show log.. Here you can check what went wrong if a certain episode is not found.