Bed bugs can come from anywhere to your house including a hotel room, old book or used furniture. But when they once come in to your house, they will show up in different ways.
You can just see one of them moving around or you can find lots of them in their hidden host like a hole or crack.
Sometimes they show up without showing themselves and they make this by biting you. You can get up in the morning with some little red points on your body and it means they bit you all night while you were sleeping.
They need blood for living and they need to bite for sucking blood. Their favorite dinner is us, human being. However, bed bugs can feed on dogs, cats or birds, their first option will always be people.