Kohlrabi is a member of the brassica family, which includes cabbage, broccoli, brussel sprouts, cauliflower and others. It can be used as a cabbage substitute, or simply sliced thin and served with a little salt & pepper (my personal favorite).
You can find a handful of additional easy, and interesting kohlrabi recipes right here
Simple Kohlrabi Leaves Pasta: Kohlrabi leaves (chopped) sautéed with bacon and onion, then tossed with pasta. Season to taste. Super easy, and super yum!