First, welcome to BYC. Second, relax! Third, some basic questions:
How many birds total, and what are their ages? Unfortunately, folks at the feed stores can be woefully ignorant. But, fortunately, there are plenty of different options for raising healthy chickens. Here's the basics, but realize that you will most likely run into feed store employees who are pretty clueless. Good idea to do some of your own research, then you can sift through the many conflicting opinions that you are likely to encounter on every single subject related to chicken care. You might want to get a good book. Save yourself some money and go to the library first. A good book: http://www.amazon.com/Small-Scale-Poultry-Flock-All-Natural-Approach/dp/1603582908. There are many others as well, but this is the most informative one I found when getting started.
Chicken feed: A hen who is laying needs extra calcium. Layer feed is about 16% protein + extra calcium. If you have a multi age flock you can provide a higher protein feed that will meet the needs of all age levels. Un-medicated starter, multi flock, or grower feed should work. Then, you'll need to offer oyster shells on the side for any birds that are laying. They will eat as much of this as they need to meet their calcium needs. This is easier to absorb than egg shells. But, you'll not want to throw those away either. I save all shells, and just toss them into the run when I have a bowl full. A quick stomp with my foot breaks them into easily shared pieces. Some folks go to the bother of washing, peeling the membranes from the inside, and even baking them. But all of this extra work is totally not necessary.
The biggest mistake folks make with their flocks: Coop and run too small. Plan on a minimum of 4 square feet/bird in the coop, and 10 sq. ft./bird in the run. Allow room for your flock size to expand a bit. Crowded flocks are prone to all sorts of behavioral problems, and more prone to illness, not to mention the extra work of keeping their space clean. The biggest mistake folks make with chicks: keeping them too warm. Check out this article: http://www.backyardchickens.com/a/yes-you-certainly-can-brood-chicks-outdoors.
Other topics to look into when you're feeling more settled: Deep litter for both coop and run. Fermented feed.
Enjoy, you're gonna have lots of fun.