[what does it all mean?]

I don't know, but it's on every hip hop record, and apparently it's New York City Mayor Fiorello Laguardia explaining the moral of a Dick Tracy comic strip over the radio during a newspaper strike (the famous sample kicks in at about 1:27).

The first use is almost certainly Double Dee and Steinski, who included it in their Lesson 1: The Payoff Mix from 1983, an astonishing sound collage.

The more you know ... Star!