I often get baffled as I think about where to use comma in the sentence and where not to do so. Examples:
1. As he left the Mayor's office , people surrounded and questioned him with serious curiosity.
2. After the meal had concluded (why is no comma used here?) the chief of police appeared on the scene .
I know that two clauses could be separated by the use of FULLSTOP, COMMA before FANBOYS, or by using the semicolon... But none of the them is used in the second sentence and also in the first sentence only comma is used and not any of the FANBOYS word after comma is used. Why?