I bought these corners online from Gardener's Supply (they come in many sizes), and then bought lumber from Home Depot. Slipped the lumber into the corners, and that was it. Raised beds! Very easy to do, although I needed DH to help me put them together. Get untreated lumber, though, if you are growing vegetables, or cedar if you want it to last longer, but cedar is much more expensive, and not readily available in the right sizes.
http://www.gardeners.com/buy/raised-bed-corners/36-643VS.html?start=6&q=corners
I love the book One Magic Square
http://www.amazon.com/One-Magic-Square-Organic-3-Foot/dp/1615190120/ref=sr_1_1?s=books&ie=UTF8&qid=1431708307&sr=1-1&keywords=One+Magic+Square
The book is full of information, but it's not fussy. She grows seeds in old toilet paper tubes, for example, uses old bottles for edging raised beds. She is very relaxed and tells readers not to worry about making mistakes, gardening is something you learn by doing. You can adapt her plans to gardens large and small.
Good Luck, OP! Having a vegetable garden is a great experience, and so much fun to eat what you grow!