When it comes to getting started with your garden, you have two choices; planting seeds, or buying entire plants. Both have their own benefits. If you plant seeds and care for them every day, you will find it is a much more rewarding experience when you have a full, healthy plant. This method is a lot more risky. I can't tell you how many seeds I've planted and never seen any trace of whatsoever.
Gardening is definitely a healthy habit though, don't get me wrong. Any hobby that provides physical exercise, helps the environment, and improves your diet can't be a negative thing. No matter what the underlying psychological cause for gardening is, I think that everyone should continue to do so. In the USA especially, which is dealing with obesity and pollution as its two major problems, I think gardening can only serve to improve the state of the world.
If you're just looking for something to look nice in your yard, you'll want a flower garden. These are usually filled with perennial flower. Perennial flowers are flowers which stay healthy year-round.
Of course I'm no psychologist; I'm just a curious gardener. I often stay up for hours wondering what makes me garden. What is it that makes me go outside for a few hours every day with my gardening tools, and facilitate the small-time growth of plants that would grow naturally on their own? I may never know, but in this case ignorance truly is bliss.