Craigslist cash buyer ad question

[Joseph Leonard]

Newbie question here: I've heard of some investors posting an ad on Craigslist saying something along the lines of "we buy houses and pay cash...". I've seen signs in neighborhoods and on street corners that say this also. 

If an investor is to go this route and is contacted by a seller, how does the transaction happen? Do you need a real estate license to do this?