Before we begin, just know you have to memorize these bad boys eventually. Sit down and do it, and it'll reward you in the long run. Crowded harbors are rife with great radio chatter using these call signs and other lingo, as this article will tell you.
Basically, every letter has an associated word with it. If you say "B" on the radio, it might just sound like "C" or "D" or anything else that ends in "eee." Radios just aren't crystal clear all the time, and this system saves potential misunderstandings.
Instead of B, it's Bravo. Instead of G, it's Golf. And so on, and so forth. So, I'm not going to pick up mooring B-G-forty-two, I'm picking up mooring Bravo Golf Four Two.
Why four-two and not forty-two? Again, simplicity avoids confusion. Every letter and number spelled out will avoid the maximum number of mistakes. Was that forty two, or thirty two? They both sound similar over a cracking radio signal. Four-two sounds like four-two every time.
To the right is a chart of numbers - you'll notice a few are different than the norm. Again, memorize this - it will come in handy! Don't be ashamed if you miss one out on the water either. Sometimes when a fellow boater is talking about whiskey, he really means he just needs a stiff drink.