A Baritone horn is similar to a small euphonium, although it's bell is angled and it's much smaller. As with all valve instruments, the 'valveings' are the same, but it's in the key of E flat. That means that if it were to play a C (open valves) then any C instrument (piano, flute, etc) would play an E flat. However, it's transpose in any B flat instrument (Clarinet, trumpet, etc).
The baritone horn like a small tuba.