Parsley
There are two main sorts of parsley: curly and flat. The curly stuff is prettier, but the taste of the flat parsley is better, so if you want to use it for cooking rather than for decoration, grow flat leaved parsley.
Growing
Parsley isn’t too difficult to grow from seed, but it does have a very long germination period (3-4 weeks), and requires warm temperatures. You’re likely to have more success starting it off inside somewhere warm than sowing it directly outside, especially if starting in spring. On several occasions I’ve sown parsley outside in spring and haven’t seen anything of it until midsummer, when the temperature finally rose high enough for it to germinate. Since the germination is a bit tricky, sow several seeds per seed pot, and remove all but the strongest seedling by snipping them off at soil level with a pair of scissors.
Once the seedlings are well-established, harden them off for a couple of days, then transplant them into their new pots. Parsley can do well in reasonably small pots, and it likes a well-drained, damp soil. It also requires nutrient-rich compost to get good-tasting leaves, so, unlike a lot of herbs, will require a certain amount of feeding. It prefers a decent amount of light (around 6 hours/day) but will tolerate partial shade.
One of the nice things about parsley is that it self-seeds like mad. So once you’ve got your first parsley plant established, it will take care of things for you after that. (This can get a bit out of hand; but you can always eat any parsley seedlings that you have to pull up!) It’s biennial, so it won’t set seed until its second full year. You’ll get a full year’s growth out of your first plant, before it flowers and sets seed at some point in the second year.
Culinary uses
Parsley is an incredibly versatile cooking herb. Its fresh flavour makes it a good addition to all sorts of meals. It’s a standard addition to a bouquet garnimix, and is used in fines herbs(a French mixture used in various dishes, which also includes chervil, chives, and tarragon). It’s used a lot in Middle Eastern cooking, and is great with chickpeas and in salads. Broadly speaking: if in doubt, add a little parsley to what you’re cooking! It is also a nice garnish, but it’s a waste just to use it for this when you could eat it as well. It goes particularly well with lemon. Chewing parsley is also said to freshen your breath after eating garlic!
Medicinal uses
Parsley has high levels of iron, carotene, and various other vitamins, so is therefore a good thing to eat in its own right. Parsley root is more often used than the leaves in herbal medicine, as a treatment for rheumatism and also to promote menstruation and relieve menstrual pain. The leaves can also be used for this, but this may be a bit less effective.
Parsley tea may help relieve bladder infections and cystitis; and can help digestion. But parsley can be a little irritating to the kidneys, and so should be avoided by those with kidney problems and pregnant women (as a medicine; it’s fine to eat in small quantities as a culinary herb).