1) Bohr makes the point that his energy levels are for "orbitals", somehow. Electrons actually orbiting like planets would create magnetic fields and slow down leading to instability of atoms.
2) The Bohr atom is for H-like (H, He+, Li2+, etc.) atoms with one electron. So each energy level is empty unless the ground state electron his excited to a higher level.
3) Later Schrodinger came up with the the Wave Equation and its solutions that correspond to all the orbitals you will learn about when you do electron configurations. At that point you will learn that 2 electrons can occupy an orbital and that electrons are acting like waves, not particles in the atom.
