I start seeds off in pots in my greenhouse propagator, although a warm kitchen shelf or window-sill is fine, around the third week of January using a peat free seed compost such as Fertile Fibre seed compost. When the first pair of true leaves are fully developed, transplant the seedlings into individual 3” (8cm) pots using a peat free compost. Alternatively, if you have used compost saved from last year then mix it 50/50 with home-made garden compost. That’s what I do. Carefully tease the seedlings out of their pots holding onto the leaves, not the stem and transplant up to the leaf joint.
Capsicums hate shock so they should always be irrigated using tepid water. Once the plants are growing on strongly and have four sets of leaves one can pinch out the growing tip to encourage a more bushy habit. By early May the plants should be ready for potting up into their final home. I use ten-inch (25cm) pots filled with a good quality peat free potting compost from Fertile Fibre or my own mix of 50% home-made garden compost with 50% used bagged compost. I also plant directly into the greenhouse border, leaving about 60cms (2 feet) between plants.
You should be able to start to pick fruit from mid July. Many chillies and peppers are delicious when eaten unripe and still green or purple. Harvest regularly as they ripen. I save chillies for the winter by freezing. I also hang up strings of chillies in the house to dry; to be ground into chilli powder or chilli flakes.