DTCS or CTSS are used to filter out the yapping of the rest of the people you are sharing a channel with.
It is using a tone or a digital characteristic to group radio's together.
Picture this:
You are in a room filled with your ex girlfriends. Let's say 10 of them . And they just found out that you cheated on all of them , so they are mad as hell. Luckily, your best friend is in the room too, although you cannot hear him due to the yapping of your angry exes.
Now you and your friend decide that both of you will cover your ears to shut out the yapping sounds, unless a specific signal is given before you start talking. Now this will result in the following situation:
When ever you or your friend talk, all the angry exes will be able to listen in on what you have to say to each other, so you still have to watch out what your are saying. But, and this is the beauty of it, when one of the the angry exes says something, you hear absolutely nothing!
In other words, you are ignoring them. Now sooner or later one the exes will find out the 'secret' signal that you and your friend agreed upon (there is only so much time you can ignore a woman) and she will start using the same signal. That will be your cue to either agree upon a new signal or better, just change rooms.
On the PMR channels DTCS / CTSS is not used in general. You can do it of course (Kenwood radio's do it), but since it is a public channel, the other people you are sharing the channel with, will still be bothered by it. Better move to another channel or create an LPD channel with a DTCS / CTSS code on it. In the download section you can find a file with 5 LPD channels with a DTCS code. Use Chirp to upload them to your radio.