Green grows better in the UK and is also better tasting imo. You may be a bit late in starting but I'd get it sown immediately. I've not grown it this year as the seeds I had were too old! I had zero germination from both red and green.
It's like celery, needs light to germinate. So wet compost, sprinkle seeds on top and wet, cover, cover with clear plastic/glass leave somewhere light but out of direct sun.
It tastes unlike other herbs imo, hard to describe
If you want another weird tasting (to typical UK tastes
) herb, next year try epazote. It smells of diesel, you use it in mexican cooking. Culantro/shado beni is another good one, used in Carribbean foods
