First, make sure you have a sunny location - 6 to 8 hours of direct sunlight. If you are putting the bed over a lawn, get rid of the lawn. Bermuda grass will come back, so if you have that, use a couple of layers of week cloth at the bottom of the raised bed before you put in the soil. I bought one of those HD kits a few years ago and it worked out well. I'm still using it several years later. As the soil settled, I added a little more. If you want to grow cool season vegetables, pick a spot that gets sun year-round, which will probably be a south facing location not shaded by your house or a tree. I just pulled out broccoli to make room for tomatoes and still have peas, cauliflower, kale and carrots.

My Square Foot Garden

you don't need raised beds to garden. You just need a spot of soil.