Burrata is a fresh Italian cheese with a surprise inside. From the outside it looks like a ball of mozzarella, and the outer shell really is mozzarella. But cut it open and the center is cream mixed with soft, stringy bits of curd. The name means "buttered" in Italian, which tells you what to expect.
How it's different from mozzarella: mozzarella is a solid ball of stretched curd. Burrata is basically a mozzarella pouch filled with cream and shreds of curd, so it's much softer and richer.
How to serve it: fresh, at room temperature, and keep it simple. It has a very mild taste and smell, so you don't want to bury it. Tomatoes, olive oil, a little salt and good bread are plenty. Take it out of the fridge a bit before serving so it's not cold, and eat it soon after opening, since it's a fresh cheese.