Secondary colours are made by mixing the two primary colours together. You can see this on the wheel clearly as the secondary colours are between the two colours that make it, for example: Blue + Yellow = Green / Yellow + Red = Orange/ Red + Blue = Purple.
On the wheel, we can see the opposite colours are situated across from each other. Blue is the opposite of Orange, Red the opposite of Green and Yellow the opposite of Purple. In terms of design/decorating, using opposite colours makes things stand out more and get noticed more. Here they are again arranged differently:
For decorating choosing three colours that combine well is best for an overall look. A good combination of colours to use are the ones that have a triangular formation within the circle. These colours compliment each other nicely.
1. Green, Orange and Purple.
2. Red, Blue and Yellow.
Outside of the Colour Wheel we encounter more colours. Black is considered a shade and is used to darken colours. White is a tint and lightens colours. These two colours should work with all other colours.
Brown and Grey are neutral colours, meaning they go nicely with most other colours. Grey by the way, is a great colour to bring out any other colours you use with it. Grey makes the other colours 'pop'.
This basic knowledge can help when choosing what colours you want put together. Keep in mind this works for all the shades of the colours, as Pink is just a White + Red, so you can follow the guidelines for Red and Peach is White + Orange, so follow Orange guidelines, and so on.
So, these are just some very basic suggestions that can be used when making colour choices. I hope you find this helpful. :-)