A single DMX channel can only control a single function of "something." That control can be a simple "on" or "off" function, or it can send an incremental signal (0% to 100% to a dimmer; actual values are 0 to 255).
Regular incandecent lights only have one electrical function: current to the filiment, which can be 0% (off) to 100% (full on). A dimmer lets you move seamlessly from 0% to 100%. One DMX channel typically controls one dimmer, a one-to-one patch. If you daisy chain any number of dimmers, they will all act in unison.
Modern LED lights used on stages usually have three or more colors of LEDs combined within a single lighting fixture. A simple RBG (red, blue, and green) LED light typically uses (at least) 4 control functions: the relative intensity of "red", the relative intensity of "blue", the relative intensity of "green", and a master intensity of the light output (like a dimmer).
More complex LED lights can have more or different colored LEDs, and can control physical movement and focus ("moving head lights", "intelligent" or "obedient" lights). As such, you might have 30 or more attributes (functions) for each LED light.
DMX channels don't care how they are addressed (numbered), but it is customary to address DMX functions on a "per light" (or group of identical lights) block of numbers. Each LED light lets you set the starting address for its group of control channels.
Lighting control boards (and software) are typically limited to the total number of DMX channels it can control.
I hope this is helpful. Good luck.