The color wheel is a circle with different colored sectors used to show the relationship between colors.
the color wheel displays the 3 primary, 3 secondary, and 6 tertiary colors.

This the Monochromactic color scheme. It is developed through adding shades of gray and black to a color to add more shades of it.

The analogous color scheme utilizes adjacent colors to create a scheme of colors 

Complementary colors use colors opposite each other. It is normally associated with a cool color and a warm color

The Triad color scheme uses 3 equally space colors on the color wheel to make a color scheme. It is often associated with a triangle

The split complementary is a variation of the complementary color scheme. It uses two adjacent colors paired with  a base color to create the color scheme. It has less tension than the complementary, but still has a high contrast.