If you can grow sweet peas, you can grow snow peas. The seeds are large, reliable and easy to plant, so there's no advantage in buying seedlings. Just get an inexpensive packet of snow pea seeds, and check the right time to plant them for your area, then put them in a sunny spot with a sturdy trellis for them to grow up - just like you would with sweet peas. When the seeds sprout, you might need to protect them from foraging birds, because the sprouts are tender and delicious. The baby plants will soon twine up their support, and in a few weeks you will see white flowers. They're not fragrant and pretty like sweet peas, but each of them will develop into a lovely crisp snow pea. Yum! Pick them when they are about the length of your index finger, and they will be incredibly sweet and delicious. At first it will take a few days to collect enough to make a meal, but keep picking them, and they will produce more and more.
It's a good idea to start a new batch of plants in another sunny spot a few weeks after you plant the first batch. It's insurance in case bad weather or inconvenient animals destroy the first batch. Also, you will need to plant a replacement for the snow pea plants, sooner or later. Snow peas won't live for more than a couple of months. The older leaves and the stems will get dried and yellow, and look mottled and nasty. When they stop producing, just pull out the old plants and put them in the compost.
You may find that you don't need to cook the snow peas, because people in the household munch them down all raw and crunchy before you get a chance.
If you do want to cook them, be sure not to overcook. Different people like different levels of trimming, and different levels of cooking. At a minimal level, you can wash them and put them in a heatproof bowl, then pour boiling water over them and leave them for a few minutes before draining and eating. Some people may want to pull or cut the tops and tails off them. Some people may want to microwave them (in water, or else they go yellow and soggy) for a minute or two. Some people may want to steam them. And they are delicious thrown into a soup, stew or pasta sauce a few minutes before serving.