To Buy: 
Look for fresh young peas with a bright green, waxy pod. Avoid yellow, split or dry-looking pods. 
Garden peas can also be bought frozen or in cans. Peas  freeze very well, holding their nutritional goodness. Avoid canned peas, they are horrible.     
To Store: 
Buy them the day you plan to eat them or the day before. Store them in a plastic bag in the crisper section of the refrigerator.
Tips & Tricks: 
500g pea pods will yield approx 1 cup shelled peas. 
Source: Stephanie Alexander (The Cook's Companion) 
Cooking Tips: 
Add the peas to a pan of lightly salted boiling water. Cover the pan and boil for 5 minutes. Drain and serve immediately.