If you are close to population, or highway, tune it to channel 19 and turn the squelch all the way down (counterclockwise) so it is making noise. Listen for voice. If you hear voice, then the receiver is working and you are getting signal to the radio.
If you have an output power meter, key the mic and see if you get full output on the meter. If it is only part way up, then it is likely an SWR problem
SWR stands for "standing wave ratio". The signal going out the antenna is a sinusoidal wave form. That is it goes positive in an arc, then back to zero in an arc, then the same negative. Looks somewhat like a half circle above and then one below.
The output circuit of the CB sends the sinusoidal waveform out the antenna. If the antenna isn't "tuned" properly, the signal is not zero when it hits the end of the antenna. If it isn't, then it will have power left and that is reflected back towards the CB. It will be of a negative polarity to that going out and will subtract electrically. This will end up causing a reflected power reading, which is read by the SWR meter. The antenna length is changed slightly to adjust so that the SWR is minimum across the 40 channels, or at a specific fregquency if desired.
Unless it is severe, it won't make the radio not work and will only effect the transmit. The receive portion should still work.
If you have metal next to the antenna, that will cause a reflected wave and make it extremely difficult to get the SWR down.
Best way is to get a buddy that has a CB and test them. Don't get them TOO close or the incoming signal will overdrive the circuitry and neither will be able to receive.
In the CB days (70--80) I have seen some units with power amps actually drive enough power into a receiver that it would make it receive even when it was switched off. But those were 1000W and 2000W linears into tune yagi antennas. Mine was only 750 watts. I had a tuned Yagi on a 40' pole and could talk about 125 miles to mobiles. But I was maintaining a mountain top repeater and had to go there alone often. So that was my means of getting back to my home base. In one case when we had it down for work in a blizzard the CB was our only communications. And that was a government site.