Analog vs Digital LED strip
Analog LED strips are either a single color (red, purple or for instance warm white) or can be RGB by using multiple tiny LEDs in all LED chips on the strip. This means the strip can only be a single color at a time and the dim level is set for the whole strip. Like this:
For Analog strips see this article for color (RGB) versions and this article for general lighting (white). Also take a look at this article why you can better get a 24v strip instead of a 12v version!
If your strip can do something like the following picture, it’s a digital LED strip and you should read this article instead. BE WARNED! A lot of sellers often show very pretty pictures with the LEDs being different colors and patterns, often this is wrong or a weird type LED strip. Analog strips can only have one color for the whole length, if you can control the individual LEDs, it’s digital: