Garlic is grown from cloves. If you are just experimenting and want to minimise expense, then supermarket bought is fine. Other wise best to buy garlic which is certified virus free - from fruit & veg supplier at �3-4 for two large bulbs.
Break bulb into cloves, plant these upright with tips just covered with soil. Plant from autumn to early spring depending on type. Prefers light, free draining soil. Full sun, sheltered from wind. Only water in very dry periods - bulb requires dry conditions to flourish. I grow in pots. Good luck !