Galaxies in the universe are intricately connected to the gas in and around galaxies. Accurately measuring the statistical properties of this gas is crucial for testing modern theories of galaxy formation and evolution. In this talk, I will present our recent efforts to characterize interstellar and circumgalactic media using integral field spectroscopy with high sensitivity in two aspects. 1) The “direct” gas-phase metallicity measurements of ISM typically suffer from ~2x systematic uncertainty, known as the abundance discrepancy factor (ADF). I will present a measurement of oxygen abundance in the nearby (3.4 Mpc) system, Mrk 71, using a combination of optical and far-IR integral field observations. Our result rules out the commonly adopted “temperature fluctuation” explanation of ADF in this object. I will also discuss the ongoing survey and the future prospects of establishing the accurate metallicity scale across all redshifts. 2) We observe Lya emission in the CGM for ~100 galaxies at z~2. We find that the Lya emission is statistically symmetric within 30 kpc, suggesting that the outflowing H I has no directional preference. Intriguingly, however, the angular dependence of Lya emission prevails from low-Lya-emitting galaxies, indicating that stable angular momentum may start to establish among these galaxies. Lastly, I will present preliminary results on the connection between the CGM Lya emission and host galaxy properties.