Learning from the chemistry of the first stars

The most metal-poor stars in the Milky Way and its satellites carry precious information about the origin and evolution of the Local group. Those ancient stars were made from the primordial material formed during Big-Bang Nucleosynthesis and polluted by very few supernovae. Their chemical signatures are key to understanding the formation of the halo, the mass distribution of the first stars, and the supernova yields. Now, thanks to the outcomes of the Gaia mission we can trace back the complex assembly of the Milky Way and interpret the information codified in the stellar atmospheres of these invaluable fossil records from the early Galaxy. We will summarize some of the aspects we could try to understand with high-resolution spectroscopy of metal-poor stars.