They're called primary colors because they can't be creaed by mixing other colors.
The secondary colors are green, a mixure of blue and yellow, orange, a mixture of red and yellow, and purple, a mixture of red and blue.
You can use light and dark colors to contrast gradients, a gradient is how dark or light a color is.
Analogous colors are next to each other on the color whel and complimentary colors are opposite each other.
Colors can dislpay moods, they can send out emotions, or trigger emotions. Wrong colors will repel some people and others will attract them.
Blue
Blue is a color of peace, wisdom, truth, honesty, or tranquility.
Red
Red is the color of love, strengh, sex, excitment, and passion.
Green
Green is a color of youth, or nature, also fertility and healing.
Brown
Brown is a color of simplicity, earthiness, comfort, or durablility.
Beige
Beige is a neutral color and it comes across well.
Black
Black is a color of death, seriousness, and elegance.
Yellow
Yellow is a bring color of illumination and happiness.
Purple
Purple is a color of dignity, royalty, or luxury.
White
White is a color of truthfulness, purity, and devotion. It's a very clean color.
Orange
Orange is a playful color and it's pleasureful and cool.
Pink
Pink is a soft color and a sweet color. It represens femininity.
Gold
Gold represents and suggests expensiveness and prestige.