Often I come across songwriters who are confused as to the labels we have for different parts of a song. It can, when written effectively, give a little change of pace to the song once the repetition begins to become obvious to the listener. Sometimes I might write a simple musical break with no lyrics, usually in the same key, but with a different chord progression. Lyrics are often part of a bridge, however. They are not as common as bridges, but can be very effective in bridging the verse just before the chorus.
Intros are at the very beginning of a song, the introduction to it.
Sometimes an intro can be effective by foreshadowing the chorus chords just a little, or a quick build of instruments into the song. When I'm playing live, I may stretch the intro to a song and let it build a groove before I start singing. Again, they can get too long and self-indulgent.