XBee Newbie needs help getting started

Can you point me to a reference for this type of thing? I feel like I will take up too much time asking you all these details, and I don't see this kind of thing on the Arduino reference page. Is "union" for example, a standard C command?

Or if you have the time, maybe you can walk me through this? I have little experience with manipulating arrays in this environment.

How do I send the number BF30CF (in hex) in four bytes over the serial interface one byte at a time, and reassemble it on the other side? Do I just Serial.print(BF), then Serial.print(30), then Serial.print(CF);? Why isn't it only 3 bytes?

I then want to use the reconstructed hex number in the command IRsend.sendNEC(0xBF30CF, 32);

Your help is greatly appreciated/