The transporter converts people and objects into energy, beams them to a destination and reassembles them, making it Starfleet's standard way to move between ships and planets.
A transporter scans the subject down to the molecular level, converts it into a matter stream and sends it to a target point, where the original pattern is rebuilt. Shields usually block beaming, and interference from radiation or unusual materials can make transport dangerous or impossible. Emory Erickson was credited with inventing the technology, which the NX-01 Enterprise used with caution.
Transporter accidents have produced some remarkable results. A malfunction split Captain Kirk into two opposing halves, a distortion field created Thomas Riker as a living duplicate of William Riker, and on Voyager a transport merged Tuvok and Neelix into a single person.
Reginald Barclay's fear of beaming led him to discover creatures living inside the matter stream. Montgomery Scott famously survived for decades by keeping himself suspended in a transporter's buffer.