I usually buy garlic bulbs from a nursery or you can use the largest bulbs from your previous year of growing. Make sure to store in a dry location to keep for next years planting.
Do NOT plant garlic in the spring. It is best to plant garlic during the first week of September. They will start to grow and then go dormant over the winter. They will then have a nice long growing season during the spring. Plant about 8 inches apart.
I usually harvest garlic on the 4th of July. When you see the tops of the garlic pointing down after about one curl you know that are ready. You can also start so see some light browning on the leaves.
Do NOT over water garlic. These plants like if fairly dry. If you over water the garlic can start to rot and turn to brown powder once they are dry. I also recommend cutting off the flower a as shown in the image above. This will give the plant more energy to focus on growing nice large garlic bulbs. I usually leave on or two flowers as indicators of when the garlic is ready to harvest.