Rather than focusing on the traditional channel list of BBC 1, BBC 2, ITV, etc TV Plus displays a list of programmes that are starting soon. This will help you quickly find a programme to start watching. It might be on a channel you wouldn't normally watch; either because it's way down the normal channel list or because it's a channel you wouldn't normally think of watching.
If you really do want to watch a specific channel, you can type in the channel's name in the search box at the top of the main programme list.