Nebular emission lines are a powerful diagnostic tool for tracing the chemical evolution in star-forming galaxies (SFGs) across cosmic time. Due to their proximity, SGFs are ideal for studying the physical properties, stellar population, and nebular gas in much more detail. The COS Legacy Spectroscopy SurveY (CLASSY) is a treasury survey that comprises UV+optical spectra of 45 local SFGs covering a broad range of physical properties. In this talk, I present the results of the physical conditions and metallicities for the CLASSY sample focused on the impact of the aperture effects of the inferred metallicities and the abundance patterns of several elements. We found that the results for the inferred electron density, temperature, and metallicity derived using different aperture sizes, 1″-3″, are consistent, indicating a uniform mapping of the nebular gas. We also showed that the physical properties derived from the optical are appropriate for observations in the far-UV, allowing a better interpretation of the interplay between the stellar and gas components. I will also discuss the results of the Ne/O, Cl/O, S/O, and Ar/O vs. O/H relations and their behaviour with different galaxy properties (e.g., stellar mass and star formation rate). We found that such abundance ratios follow a constant trend with O/H as expected, except for Ne/O and Ar/O, which show a significant trend at high metallicities. We discuss the scatter involved in the N/O versus O/H relation and its connection with the different UV+optical observables. Finally, we compare these results with the chemical abundances derived at z > 6 galaxies observed with the JWST.