Barre chord
fret 1, A shapex13131
B♭7 is the B♭ dominant 7 chord. Its notes are B♭, D, F and A♭. It is the same chord as A♯7. A major triad with a flat seventh. Try G7 resolving to C.
x13131
686766
Numbers show frets from the low E string to the high e string; x means don't play that string.
B♭7 is the V7 chord in E♭ major. That makes it a natural fit in songs written in those keys.
Every B♭, D, F and A♭ on the first 12 frets. The filled dots are the root, B♭. Build your own shape from any nearby group.
Other B♭ chords
Other dominant 7 chords