To make things simple, CSQ is Carrier Squelch. Squelch is basically something that opens a radio system and allows transmissions thru the system. With Carrier Squelch, the system is always open and any radio transmissions received on that frequency will be heard. There is no PL or DPL tone to regulate the transmissions, or open and close the squelch.
This is why PL & DPL tones are most effective for those of us who have scanners.
An example: Town A and Town B. The police dispatch frequency for both towns is 154.450. You program Town A in channel 1 in your scanner and Town B in channel 2. Town A (channel 1) is CSQ and Town B (channel 2) has a PL of 151.4. You will only hear Town B on channel 2, because it has a PL tone, but on channel 1 you will hear both because it will receive any transmission on that frequency. There is no PL tone to block out the other channel.
The only difference in programming the CSQ frequency is that you don't put a PL or DPL tone in, because it doesn't have one.
Hope you understand a little better.
Good luck and continue to enjoy the hobby.