How do you make a raised bed for gardening?

Image by suburbandollar
This is one of two raised beds I am using to grow vegetables this year. As you can see I have sectioned the bed off into square foot sections for use in the square foot gardening method of growing.

Along the backside of the bed there is a vertical trellis made up of galvanized piping and nylon netting.

Question by Gran Gran: How do you make a raised bed for gardening?
My granddaughter want to make a garden in a boxed area. What is the best method for making a raised garden bed?

Can you help? Leave your own answer in the comments!