About the Bbdim chord
To play Bb diminished, use the first shape above. Place your index finger on the 1st fret of the C string, your middle finger on the 1st fret of the A string, and your ring finger on the 3rd fret of the G string. Leave the E string open. Strum all four strings and check that each one rings cleanly.
Root
Bb
Quality
Diminished
Notes
Bb · Db · Fb
How the Bbdim chord works
Bb
Root(1)
The home note. It gives the chord its name.
Db
Minor third(♭3)
The defining minor interval above the root.
Fb
Diminished fifth(♭5)
A lowered fifth that adds harmonic tension.