Peak and tune are often used interchangably by many CB-ers. Tuning refers to adjustment of the various internal adjustments for best performance. Peaking tends to mean the same thing, but with concentration on transmit performance. "Swing" is referring to the increase in output power seen when you talk into yoour microphone. You should take alot of what you hear about "swing" with many grains of salt, since there is a TON of mis-information all over the Internet, and in alot of printed material as well.
As for swing kits (also called mod or modulation kits), in general they should be avoided. They are generally intended to give your radio a low output when just keying your mic, and a much higher output when speaking. While this looks great on most power meters, careful scrutiny of the signal from an audio and form a technical point of view will show that the signal becomes distorted when you try to go past a certain point.
The parts you see in various modifications could be parts that are intended to be added, or parts to be taken out. In general (with a few exceptions), mods which recommend completely removing a part (or parts) are NOT good mods. One exception is the procedure for converting a CB from a regular final output transistor to what is called an FET (Field Effect Transistor).
As for knowing what those parts are, thats where alot of study, reading, and schooling comes into play. If you're serious about wanting to learn, then start with basic electronics courses at your local technical college, or read and study books on basic electronics.
