Despite the long history of the study of superconductors, probing their collective modes has only recently garnered interest, especially via Raman spectroscopy and pump-probe experiments. This is largely due to the multi-component feature of the newer superconductors arising from the band/orbital/valley degrees of freedom. Not only is there a wider range of collective modes in such situations, the information they carry is also crucial towards understanding the nature of electron correlations. In this talk, we will discuss what these collective modes are, what it means when they show up with a certain spectral weight, and how they couple to different observables. We will demonstrate the validity of the work by explaining the Raman spectroscopy data in Fe-based pnictides and chalcogenides, and offer some predictions for non-linear effects such as the third-harmonic generation.