In response to Jessica's question about getting started and number of seeds:

I'd really recommend the Square Foot Gardening book (the 2006 revised edition) for most of this - it walks through everything in a simple, yet detailed way.

However, you can start here for a summary: http://www.squarefootgardening.com/index.php/The-Project/how-to-square-foot-garden.html

For a cheap-and-easy way to get started, take two 8-foot boards (6/8/10 inches wide).  Cut them in half (yielding four 4-foot lengths). Screw those together at the corners to form a square frame.  Then fill the frame with soil and you have a basic raised bed.

For planting, divide the space in the frame into square-foot blocks.  (For example, if your box is 4 ft x 4 ft, you'll have 16 squares.)  Each of these squares is for a crop; the number of seeds that goes into that square varies depending on the plant (generally 1, 4, 9, or 16).  There is detailed information about plants-per-square in the appendices of the book; there's also a useful summary and visualizations here: http://www.essene.com/Vegetarian/PlantSpacingsInASquareFootGarden.htm.

My planting schedule also includes some notes about spacing (the small notations that say 4/sq, 9/sq, etc.).

See also the FAQ on the Square Foot Gardening website for information to specific questions, getting started, plant spacings, etc.

-- Andy

Jessica, I have almost all the square foot books from the library in case you're having trouble getting them.  I'll bring them next time I see you for you to look at -- I think they are probably on hold for other people that want them, too, so when I return them, they may not be readily checkout-able. 

And I think the link that Andy provided for the Web site is really helpful.  My philosophy is, too, if we think about planting a garden but not over think it, then our natural need to cultivate and grow food may come out of us just based on the inborne need to survive.  ("Something" taught a caveman to make a tool and a mother to nurse a baby.)  So if we make a mistake with something we plant, great!  We won't make it next time...but share with others what you have learned either way.