Snap peas are eaten whole, unlike greens peas that need to be shelled. They are also different from snow peas (pois gourmands) which are flat. They should be really fresh, as peas do not save more than a couple days. My friend Paul Vigneux has been known to literally run with the peas from his garden to the boiling pot*. If you have time, break the top end off and pull on it to remove the thread along the body of the pod.
So you have a steamer boiling, add the snap peas and cover for four minutes, no more, no less. The peas will be bright green, crunchy, tender. Eat plain or with a little bit green onion sautéed in butter. Easy on the onion as the snap pea flavour is delicate. Salt!
*Paul corrected me saying that the actual reason he was running was that it started raining!