Rabbi means "teacher", but rabbis are also clergy people who can do other things:1. Write books2. Kosher food supervision3. Religious counseling4. Religious school principals5. Religious camp owners
Yes, in order to use the title of 'Rabbi', a person must receive their 'smicha' through a Jewish religious school (Yeshiva).
A rabbi by Hebrew definition is a teacher. But really, it's more reffered to someone who teaches Judaism. I should know, I'm Jewish!
A rabbi is a Jewish cleric.
Perform interfaith marriages.