A garage is a building that's meant for keeping cars or other vehicles in. Some houses have attached garages with automated doors.
You might have your own garage, or you might pay to park your car in a large public garage down the street. The two buildings are very different — one large enough for one or two cars, and the other possibly accommodating hundreds — but they're both garages. You can also use the word garage for a car repair shop: "I have to take my car to the garage because it's making a weird noise."