Bridges are one way to replace missing teeth. Your existing teeth are used to support a "bridge" of connected crowns to span the area where your tooth is missing. You will wear a temporary bridge while the lab fabricates your permanent bridge. You will then have a follow-up visit to cement the bridge.
If you are missing a tooth you should strongly consider having it replaced. Besides the esthetic disadvantage of missing a tooth, the adjacent teeth may also shift into the space, causing problems with your bite. If the teeth supporting the bridge do not require crowns, replacement of the missing tooth is often possible with dental implants.
The pictures below show a three unit all-porcelain bridge. The crown in the middle (the "pontic") replaces the missing natural tooth and is supported by the teeth on either side (the "abutments").
Side view of a 3 unit bridge