What exactly makes an "RF amplifier" different from any other amplifier?

The only other type of amp I have built is with small transistors for an audio signal, and even then I didn't really understand how to calculate what resistances I need.

Also I have a couple TIP42 power transistors that I was hoping to use to amplify the signal output but I'm not sure exactly how to go about designing the proper circuit.

Any help or a point in the right direction would be greatly appreciated!