RF gain adjusts the RF amplification on the receive side. It's really not too much use on a CB. It is generally used for SWL to help eliminate noise and dig signals out of the background.
The method of useing it is; first find a channel in use, then turn RF gain all the way down, then volume all the way up. Start turning the RF gain up till you can hear those talking again. You should notice less hiss and background noise.
Squelch compleatly cuts the volume until a certain signal level is reached, then audio comes back.
If you are getting reading to check your SWR, then the transmitter is working. Usually an all or nothing situation.
Normal range 4 - 5 miles with a decent antenna.
A lot of people out there just won't answer a "radio check". Your a new guy, they don't want to talk to you. I don't know why, just the way it is. Best to have a buddy help you.