since each frequency corresponds to a particular energy, the nature of this spectrum implies that the atom can only lose energy in certain fixed amounts. This in turn leads to the conclusion that the electron in a hydrogen atom can only exist at particular energy levels.

why can electrons only exist at specific energy levels?

and what do it mean by specific energy levels?

what do it mean by frequency corresponds to a particular energy?

i understand there's the first energy level and the second energy level but hydrogen atom only has 1 energy level, so im confused.