A telescope gives magnified views of the Earth and the sky. As such, its field of view is very narrow. Pointing the scope at a distant object on the ground or a small, faint object in the sky can be difficult.
This is where a small telescope or another kind of pointing device mounted on the side of a scope can be a great help. Like the riflescope on a rifle, the pointer is aimed parallel to the main telescope and provides a low-power view that is easy to point at the target.
A finderscope is a small refractor or lens-type telescope. The aperture is typically between 20 mm and 50 mm with an eyelens or eyepiece providing powers in the range of 5x to 10x.