The hydrogen spectrum is basically an important piece of evidence for showing the quantized electronic structure of an atom.
When the Hydrogen atom will absorb a photon, there will be a transition of the electron to a higher energy level .
When the Hydrogen atom will emit a photon, then there will be a transition of the electron from the higher level to the lower one.
When the transition of the electron from higher to lower levels takes place, the transmission of light or radiation will happen.
So, the quantized energy levels of the atoms will cause the spectrum to comprise the wavelengths that will reflect the differences in the form of these energy levels.