Presented here are four studies in which the strong gravitational effect is used as a tool in studying the physical properties and environments of galaxies with an emphasis on dusty star-forming galaxies at high redshifts. The first chapter contains an introduction to the dissertation. In the second chapter we present Hubble Space Telescope (HST) WFC3 imaging and grism spectroscopy observations of the {\it Herschel}-selected gravitationally-lensed starburst galaxy HATLASJ1429-0028. It is found that a combination of high stellar mass, lack of AGN indicators, low metallicity, and the high star-formation rate of HATLASJ1429-0028 suggest that this galaxy is currently undergoing a rapid formation. In chapter 3 we present a source-plane reconstruction of a {\it Herschel} and {\it Planck}-detected gravitationally-lensed dusty star-forming galaxy (DSFG) at $z=1.68$ using {\it Hubble}, Sub-millimeter Array (SMA), and Keck observations. We present a lens model with source plane reconstructions at several wavelengths to show the difference in magnification between the stars and dust, and highlight the importance of a multi-wavelength lens models for studies involving lensed DSFGs. We find the ratio of star formation rate surface density to molecular gas surface density puts this among the most star-forming systems, similar to other measured sub-millimeter bright galaxies (SMGs) and local ultra-luminous infrared galaxies (ULIRGS). In chapter 4 we make use of FIRE-2 cosmological simulations in order to model the light coming from sub-millimeter bright galaxies and quantify the effect of differential magnification. We compare the results to observation and find that there is a physical offset between the light coming from stars and the light radiated by dust in the simulated galaxies that is in agreement with observations. Having the source and lens be physically offset, having the lens be closer to the source than the observer and increasing the mass of the lens all contribute to a greater magnification of the stellar light vs. the dust emission intensifying the differential magnification effect. When deriving the physical properties of galaxies from model SEDs we find that the overall effect of differential magnification is an underestimation of the ratio of star-formation rate to stellar mass that is equivalent to the ratio of stellar magnification to dust magnification. In chapter 5 we measure the Cosmic Microwave Background (CMB) skewness power spectrum in {\it Planck}, using frequency maps of the HFI instrument and the Sunyaev-Zel'dovich (SZ) component map. We model fit the SZ power spectrum and CMB lensing-SZ cross power spectrum via the skewness power spectrum to constrain the gas pressure profile of dark matter halos. The gas pressure profile is found to be in agreement with existing measurements in the literature including a direct estimate based on the stacking of SZ clusters in {\it Planck}.