i have grown a green chilli plant and have 4 big chillis on it now. does anyone know when i should pick them and do i hang them up to dry or what? should they turn red? i dont know!

not sure if their like normal peppers that go from green to red but i would pick them and either keep yhem in the fridge and use fresh or you could leave them in a dry warm place to to dry our by themselves.
i usually put them in a bottle of olive oil, just prick them first and you have chilli oil to use for cooking.

Green chili peppers don't turn red, although some may flush an orange colour as they ripen--depends what you are growing. There are so many different kinds, not all of them for culinary use. We had an elderly Pakistani man on our allotment site who grew nearly 200 different cultivars.