I'm sorry but I still don't understand the concept of spectral analysis and the baseline. What does these words mean and what are they for? I'm confused...

Note: the experiment determines the concentration of iron in iron(II) phenanthroline by spectrophotometry.

Spectrophometery is the measurement of how much light (or infrared radiation) passes through a clear sample (usually a liquid) as a function of wavelength. Every material will have a certain spectral "fingerprint" in the resulting graph of absorption (or transmission) vs. wavelength. The strangth of the amount of absorption at certain characteristic wavelengths of a compound reveals how much of that compound (such as iron (II) ) is present in the sample.

As far as the meaning of "baseline" is concerned, I would have to know more about the sentence in which it was used. It may refer to the light signal vs wavelength for an empty cell.