A Bb at the start of a key signature means you play all ''B notes'' as Bb, not plain B.
When typing, you can use the letter b to signify a flat. For example: Bb would mean B-flat.
E flat consists of 3 flats, B flat, E flat and A flat. E flat to B flat would be a perfect 5th interval as B flat is in E flat major, but because your question was E flat to B, B is a semitone up from B flat, this would mean the interval becomes a semitone larger, and a semitone larger from a perfect interval is augmented. Therefore, the answer to your question is an augmented 5th. Hope this helps :)
it means B flat on the piano
It depends on what scale you're talking about. B flat major = B flat, C, D, E flat, F, G, A B flat harmonic minor (ascending and descending) = B-flat, C, D-flat, E-flat, F, G-flat, A (natural), B-flat, A (natural), G-flat, F, E-flat, D-flat, C, B-flat B flat melodic minor (ascending and descending) = B-flat, C, D-flat, E-flat, F, G (natural), A (natural), B-flat, B-flat, A-flat, G-flat, F, E-flat, D-flat, C, B-flat B flat natural minor = B-flat, C, D-flat, E-flat, F, G, A, B-flat
F A flat B flat F A flat B B flat F A flat B flat A flate F
For b flat major: b flat, c, d, e flat, f, g, a, b flat. For b flat natural minor: b flat, c, d flat, e flat, f, g flat, a flat, b flat. For b flat harmonic minor: b flat, c, d flat, e flat, f, g flat, a, b flat. For b flat melodic minor, ascending: b flat, c, d flat, e flat, f, g, a, b flat. (Melodic minor descending is the same as the natural minor.)
B-flat
Bb is B flat as typed on a keyboard.
Every key signature that has flats has a B flat. These keys are: -F Major (Also D Minor and G Dorian) Has only B flat. -B flat Major (Also G Minor and C Dorian) Has B flat and E flat. -E flat Major (Also C Minor and F Dorian) Has B flat, E flat, and A flat. -A flat Major (Also F Minor and B flat Dorian) Has B flat, E flat, A flat, and D flat. -D flat Major (Also B flat Minor and E flat Dorian) Has B flat, E flat, A flat, D flat, and G flat. -G flat Major (Also E flat Minor and A flat Dorian) Has B flat, E flat, A flat, D flat, G flat, and C flat. -C flat Mojor (Also A flat Minor and D flat Dorian) Has B flat, E flat, A flat, D flat, G flat, C flat, and F flat.
C minor
B flat C D E flat F G A B flat
B-flat and E-flat are found in B-flat major and G minor.