Cabbages can be grown from seed, using a propagation tray or jiffy pots, or you can buy seedlings from most nurseries between April and August.
Plant your seedlings by mid-Autumn. Leaving them until winter can result in it being too cold for them to get good early growth.
Cabbages are generally slow but steady growers. They get very green and leafy over two months and then almost overnight, start to develop the veg bit you want. They develop into edible cabbages in about 2 weeks.