Question

What is the empirical distinction between emission and absorption spectra? In general terms, how did Niels Bohr explain each of these spectra?

In general terms, emission spectra are obtained when the electron is at a high energy level and it falls to a lower energy level. In absorption, the electron is at a lower level, absorbs energy, and is raised to a higher level. As to how Niels bohr explained all of this, I refer you to your text. Look at the Balmer series (and other series) and how Bohr explained that.