Canon use the "-S" suffix to indicate a lens or camera which is designed for a so-called "crop" sensor, also called APS-C, roughly equivalent to Super 35. As opposed to "full-frame", which has a larger sensor.
So a "-S" camera will have a sensor about 23mm × 15mm. A "-S" lens will create an image big enough to cover that sensor, so it will work fine. A full-frame lens -- i.e. no "-S" -- will create a larger image, which will also be fine.
A full-frame camera -- i.e. no "-S" -- will have a sensor about 36mm × 24mm -- quite a bit larger. A full-frame lens will cover this no problem, but a "-S" lens will not. The camera will handle a "-S" lens by reading out only a part of the sensor ("crop mode"), which will give you a drastically reduced resolution. Your pictures will be OK, but with nowhere near the resolution you paid for.
The benefit of a "-S" lens on a "-S" camera is that it will, in general, be smaller, lighter, and cheaper than a full-frame lens; the drawback is that if you later upgrade your camera to full-frame, then the "-S" lenses won't work well.
A "-S" camera, or a full-frame camera in crop mode, will also have a narrower field of view; so your lenses will all be a bit more telephoto. Multiply the focal length by around 1.5 to get the "equivalent full-frame focal length". So a 100mm lens on a "-S" camera is still a 100mm lens, but will give you the field of view that a 150mm lens would give you on a full-frame camera.
If you want to know more about lens mounts, I wrote an article which tries to explain this stuff: https://moonblink.info/MudLake/gear/lenses
Hope this helps.
