FREE: Ornamental Cabbage Seeds, Purple/Pink/White Slow Bolt

Yes, you can eat them. I dont think they are as tasty as the reg. cabbage though.
Here are the instructions on growing them.
Growing Kale and Ornamental Cabbage from Seed.
Kale seeds require light for germination, so DO NOT COVER THEM with soil.
It is best to sow Kale seeds directly into the garden, where they are to grow. The exact timing for sowing and planting will depend on your local conditions.
Sow Kale seeds about six to ten weeks before the first anticipated frost.
Plant the seeds in rows, spaced 18 to 24 inches apart, allowing 6 inches between seeds. Keep the soil moderately moist during germination.

The seeds will germinate and sprout in one or two weeks, depending upon weather and soil warmth.
When the young plants are about 3 inches tall, thin them out leaving the strongest and best plants spaced about 18 to 24 inches apart.
Although Kale and Ornamental Cabbage seeds can be sown indoors at any time of the year, without cool temperatures the plants won't attain much color. For starting seeds indoors, I recommend that they be sown directly into a large 6-8 inch pot, to avoid the problems associated with transplanting.
Once the seeds of Ornamental Cabbage are sown, place the flat or pot in the refrigerator for 3 days to expediate germination.
Flowering Kale does not need this pre-chilling period.