Screw starters are hand-held tools that are used for starting or removing screws. They're ideal for use with screws that are in hard-to-reach places, or for screws that are too small to hold by hand. Different models are designed for slotted or cross-head screws and many come with a handy magnet on the end.
Screw starters have a small chuck (a type of clamp used to grip an object) at one end. The chuck opens, usually by the twist of a handle, and the head of a screw can be inserted. Closing the chuck secures the screw and holds it firmly in place until it's released. Once you've started the screw you can release the screw head with a simple twist on the starter tool and use a regular screwdriver to finish screwing or unscrewing.
Screw starters are particularly helpful when you're working in an awkward site or with very small screws that could easily be dropped. They can be used for a variety of domestic jobs including installing a switch plate for an electrical outlet or assembling furniture.