Gardening Beginner

So, I'm going to start venturing out and trying new things. First on the list, growing a garden. I have quite a brown thumb...I tend to kill all the plants in my house, so I'm not sure how this is going to go. I bought my first packs of seeds today and I'm not sure that was the right decision. Should I buy the seeds or the plants already started? Should I plant the seeds now in small pots so they are small plants when it is time to put them in the ground? How is a girl supposed to know all of this stuff? Well, the lady across the street seems to know a little bit about everything...actually, she thinks she knows A LOT about EVERYTHING. Anyways, she's a good neighbor to have and I'm thankful for her being on my neighborhood watch. Regardless, she is apparently on-board assisting me in getting my garden up and running. I want to have tomatoes, cucumbers, green peppers, green beans, peas, watermelons, squash, etc, etc, etc. I LOVE FRUITS AND VEGGIES!!! It makes my mouth water just thinking of all of the fresh stuff I will have this summer and fall.

So, where to start? I've read a few things on mapping out your garden and such, so I think I will start there. Dad is coming next week, maybe, so I think he may help me get the soil ready. With this crazy weather we are having, who knows when I will actually be able to get the plants in the ground.
Do you have any helpful hints for me? Truly, people, I'm up for trying anything. Do I need to add anything to the soil? What type of seeds should I use? Let me in on the gardening scoop...I appreciate your help and will keep you posted on the progress. Bring on this challenge!