Value is a pretty simple element of design to understand and use when making your artwork. It is referred to as the measure of light and dark in a color. Value in certain cases can also help convey emotions and ideas. The use of value strongly with contrast, you can have high contrast with a very light color and a dark color, or you can have low contrast with two similar colors. Value can also correlate well with emphasis drawing your attention.
Before understanding value within colors, it might be a good idea to master the idea in black and white first. It is better to start out with a smaller selection of color to become familiar with how value can affect your artwork, and it is a lot less overwhelming. You can start by making your own value scale, drawing out about ten boxes. You then take a few different pencils, one about 6B and another light one like an HB and shade each box with the darkest color on one end and the lighter one on the other. This is a good exercise to do when starting out with using value.
Value is also great to understand for shading purposes because then you know how lights and darks fall on objects. This makes it easier when drawing, take for example how a shadow would fall on a square from a light source. Depending on how intense/close the light source is, you can shade it using values that would correspond to that light source.