The Universe began with a simple chemical composition of hydrogen, helium, and a small amount of lithium. Since then, this composition has evolved thanks to nucleosynthesis events. Low-mass stars serve as fossil records of these chemical enrichments, as their surface composition remains largely unchanged throughout their long lifetimes. In this talk, I aim to demonstrate how stellar chemical abundances can enhance our understanding of stellar populations in the Milky Way and the origin of elements. I will focus on the stellar halo of the Milky Way, where we can observe stellar populations that formed outside the Milky Way and those that formed in the early Universe. I will first review recent progress in this field, particularly on the discoveries of spatial and kinematic substructures from Gaia data. Next, I will discuss the astrophysical implications derived from the chemical abundances of stars in these substructures, including insights into the host of a 33 solar-mass black hole, disrupted globular clusters, and the Milky Way's galaxy accretion history. I will emphasize that high-precision chemical abundance measurements are crucial in obtaining these insights. Finally, while characterizing stellar populations through chemical abundance relies on our knowledge of nucleosynthesis, I will illustrate that observational constraints on chemical enrichment histories of stellar populations provide valuable constraints on the origin of elements. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09