The B Button is the large trigger on the underside (back) of the Wii Remote.
[Power] ◄ Home ► │ [1] [2] ◄ A (Front Face) ► │ [+] [-] ◄ - + ► │ [B] ◄────────── TRIGGER (Index Finger)
Remember: A (Front) = Confirm / Primary Action. B (Trigger) = Back / Secondary Action / Trigger.