There are three main models to numerically model a color space.
There is an additive color mixing model, which is basically your standard RGB model, where you basically control how bright each of the red, green, and blue lamps shining at a point. There is a complementary subtractive color mixing model, which is controlling the amount of pigments you drop onto a substrate (CMYK is what you'll see used in computers these days). Then there's a third model, where you measure it according to brightness, colorfulness, and then the actual hue it is--there's a lot more variants in this model, basically any colorspace you don't recognize is this kind of model.
If you visualize colors existing in an RGB cube, you have 8 colors at the vertices: black and white are at opposite ends of a diagonal, and the other 6 are two sets of nonadjacent vertices: red, green, and blue in one set, and cyan, magenta, and yellow in the other set. Given such a cube, you should be able to easily see that RGB is using one of those sets as its basis set, whereas CMYK is using the other set as its basis set. The third set of models is built by tilting the cube such that the black-white diagonal is now the vertical line (one of the components), and then distance from this line becomes another component, and then the angle around the line is the final component--it's a cylindrical coordinate space in 3D space, not a Cartesian space.
Some models, like CIELAB or Oklab, use the third model but retain a Cartesian coordinate system, the last two values being called something generic like 'a' and 'b'. Oklch is the same as Oklab, but expressed as cylindrical coordinates, because chroma (colorfulness aka distance from the pure light line) and hue (aka the dominant color of the light) is more convenient for people to work with than a Cartesian system.
There is an additive color mixing model, which is basically your standard RGB model, where you basically control how bright each of the red, green, and blue lamps shining at a point. There is a complementary subtractive color mixing model, which is controlling the amount of pigments you drop onto a substrate (CMYK is what you'll see used in computers these days). Then there's a third model, where you measure it according to brightness, colorfulness, and then the actual hue it is--there's a lot more variants in this model, basically any colorspace you don't recognize is this kind of model.
If you visualize colors existing in an RGB cube, you have 8 colors at the vertices: black and white are at opposite ends of a diagonal, and the other 6 are two sets of nonadjacent vertices: red, green, and blue in one set, and cyan, magenta, and yellow in the other set. Given such a cube, you should be able to easily see that RGB is using one of those sets as its basis set, whereas CMYK is using the other set as its basis set. The third set of models is built by tilting the cube such that the black-white diagonal is now the vertical line (one of the components), and then distance from this line becomes another component, and then the angle around the line is the final component--it's a cylindrical coordinate space in 3D space, not a Cartesian space.
Some models, like CIELAB or Oklab, use the third model but retain a Cartesian coordinate system, the last two values being called something generic like 'a' and 'b'. Oklch is the same as Oklab, but expressed as cylindrical coordinates, because chroma (colorfulness aka distance from the pure light line) and hue (aka the dominant color of the light) is more convenient for people to work with than a Cartesian system.