  The embedded phase of star formation is the crucial phase where most of the
stellar mass is assembled. Velocity-resolved spectra reveal an infalling
envelope, bipolar outflows, and perhaps an infant circumstellar disk -- all
locked together in a cosmic dance of gravitational collapse and magnetic winds.
Densities and temperatures change by orders of magnitude as the protostar
evolves, driving a chemistry as exotic as it is fascinating. I will review two
examples of how to exploit chemistry and molecular spectroscopy to study the
physics of low-mass star formation: energetic feedback and episodic accretion.
