Shuttles are small space craft often carried internally by larger starships. They allow people to move from the ship to another location that's out of the range of Transporters.
Shuttles are often used to transfer personnel between ships, stations, planets and other locations.
Most Shuttles do not have interstellar range. Even the ones with Warp drives are extremely limited in range, usually to a single solar system useful distance.
Larger craft that have interstellar range called "Warp Shuttles" or "Runabouts".
Smaller shuttles, called "shuttlepods" carry fewer passengers and have much shorter range, usually enough to go from orbit to the ground and then return. They are used for close range destinations, or for on-orbit work.
Shuttlecraft allow the characters in a story to move from the ship to the site of a story, this often places the characters out of range of easy back up from the ship and crew.
Sometimes these are used as vehicles to inject new characters and their stories into the existing ship and crew.
This can be flipped - a shuttle may take central characters into another scenario with its own batch of characters and involve our heroes in their story.
The dramatic key to a shuttlecraft is that it separates the characters using it from their ship, and offers them very little in the way of techno-magic leverage to use in solving problems.