Function of collimator , turn table, telescope

I m in 11th class it can in a federal board paper plZz answer according to the book but easy and right......)

The question of Spectrometer is very very important as it came in my exam too of Balochistan Board, Quetta dated April 23, 2013.
Spectrometer consists of three parts
(i) Collimator
(ii) Turn table
(iii) Telescope
Actually, the light from some source enters the collimator, passes through it, enters turn table where a diffraction grating is present. It splits the white light into several colours (spectra). It also directs the light into the telescope where a convex lens is placed which converges the spectra to the eyes of observor.
Spectrometer is a device which is used to study the spectra.
So the functions of collimator is to direct the light to the turn table.
Function of turn table is to split the light into different colours.
Function of telescope is to make the observer observe the phenomenon.
Wish you a very best of luck.