Sweet peas are grown from seed (you can get seedlings if you forget to plant them in time) in Autumn. They grow through Winter and flower in Spring and into Summer.
Sow in full sun, about 20 cm apart. Bury the pea well, as birds favour them. Plant in well-drained soil, and give them a little fertiliser as they grow. You will need to plant them against a wall or train them along a trellis.