While garlic is best planted in the fall, it's not too late to stick some in the ground if you hurry! Garlic is one of those healthy, sustainable crops that not only do you good, they're good to grow. If you forget them or miss a bulb or two, they'll be back the following year.
I read on the package of the elephant garlic I just bought for seed that it's good to mix a little sand with your soil so they can expand easily underground. This is true of any root crop, if you live in an area of clay or dense soil. However, don't make it too loamy and loose. A little wood ash or lime will help build up a little potash and calcium that root crops love.
You can break apart a bulb and plant each of the individual cloves, root part down. If you've kept the bulb until spring, you might see a little green shoot coming out the top--a plant wanting to grow. I don't know about planting grocery-store bulbs. It seems like they would grow but without knowing their provenance, I'd go with heirloom, local garlic if possible. Otherwise, go to a seed exchange or one of my favorites, Baker Creek Heirloom Seeds.
Garlic will bloom in summer--at which time you can cut off the blooms (also called "scapes" and cook with them--a delicate, garlicky flavor). The garlic can be harvested at this time if you want to eat some, but the bulk can be left in the ground so the husk can develop. As long as the top is removed, the plant's energy will go into making you a bigger garlic bulb to eat later. They keep well and if you harvest before the fall dampness, you can count on getting a year's storage. Some of the bulbs shrivel but you can save those for seed, and though it's hard to resist, you'll want to save a number of your best bulbs for planting that fall. You can either immediately replant or even wait until late fall, just before the ground gets hard.
When saving seed, think of it this way--a typical bulb might have six cloves, so if you want, say, 60 garlic bulbs next year, you'll want to save 10 bulbs.
Garlic is famous for its folk value in "medicine." Though of course I'm not a doctor (merely a practitioner of love), it's historically been used to stave off colds and other viruses, boosts immunity, and is said to lower blood pressure. Besides cooking, if I feel a grunge coming on, I'll eat a raw clove or two (in conjunction with other preventive measures we'll explore later). Garlic. It's good, good for you, and keeps vampires away.