Neither of the above answers is correct. A bridge is just another name for the B section - most songs are constructed in AABA form. You compose an 8-bar section of your main melody. You repeat it. You write something that contrasts, yet blends - and often has different chord progressions, or is in a neighboring harmonic area, like subdominant (if you started in D, it would be in the key of G.) The end of the bridge gets you back into the setup for the return of the A section - often by using a double dominant or 5 of 5 chord. They you have the A section again - so a total of 32 bars, AABA form. Standard for all pop tunes since the earliest days of recoding - when you had to get it done in 3 minutes (old 78 RPM records).
Folk music is more likely ot have verse/chorus structure - each vers has different words, but the chorus is always the same. Form is ABABABABABAB. Easy for the crowd to join in.
Music director since 1971.