Basically, a spectrometer takes in light, separates it into its spectral components, digitizes the signal as a function of wavelength, reads it out and displays it through a computer.
It is then collimated by a concave mirror and directed onto a grating.
The grating disperses the spectral components of the light at slightly varying angles, which is then focused by another concave mirror and imaged onto the detector.
From the detector, data can be obtained through a software, which can be used for spectroscopic manipulations.
*Terms:
Diverge: deflect (light rays)
Collimate: to make (light rays) parallel