The rest-frame UV spectra of Lyman Break Galaxies (LBGs) at z ∼ 3 are analyzed to study their spectroscopic properties. A database of nearly 1000 LBG spectra is used to create high S/N composite spectra, revealing features from hot stars, H II regions, dust, and outflowing gas. Grouping the data by galaxy parameters like Ly α equivalent width, UV slope, and kinematics isolates major trends. LBGs with stronger Ly α emission have bluer UV continua, weaker low-ionization absorption lines, smaller kinematic offsets between Ly α and interstellar absorption, and lower star-formation rates. There is a decoupling between the dependence of low- and high-ionization outflow features on other spectral properties. Galaxies with rest-frame W_Lyα ≥ 20 Å have weaker high-ionization lines and stronger nebular emission lines. These trends are explained by large-scale outflows. The appearance of LBG spectra is determined by the covering fraction of outflowing neutral gas and the velocity range of this gas. Collisionally excited nebular emission lines are not affected by outflow, and variations may indicate differences in H II region temperatures and metallicities. Higher sensitivity and resolution are needed to fully understand outflow properties and their relation to Lyman continuum escape. The study highlights the importance of understanding LBGs' outflows and their impact on the intergalactic medium. The composite spectra show a wide range of spectral features, including stellar photospheric lines, interstellar absorption, nebular emission, and outflow-related features. The analysis of these features provides insights into the physical conditions of LBGs, including their star-formation histories, metallicity, and outflow dynamics. The study also addresses the potential contribution of AGN to LBG spectra and the abundance ratios of C/O and O/H in LBGs. The results emphasize the need for further observations to clarify the physical processes governing LBGs at high redshift.The rest-frame UV spectra of Lyman Break Galaxies (LBGs) at z ∼ 3 are analyzed to study their spectroscopic properties. A database of nearly 1000 LBG spectra is used to create high S/N composite spectra, revealing features from hot stars, H II regions, dust, and outflowing gas. Grouping the data by galaxy parameters like Ly α equivalent width, UV slope, and kinematics isolates major trends. LBGs with stronger Ly α emission have bluer UV continua, weaker low-ionization absorption lines, smaller kinematic offsets between Ly α and interstellar absorption, and lower star-formation rates. There is a decoupling between the dependence of low- and high-ionization outflow features on other spectral properties. Galaxies with rest-frame W_Lyα ≥ 20 Å have weaker high-ionization lines and stronger nebular emission lines. These trends are explained by large-scale outflows. The appearance of LBG spectra is determined by the covering fraction of outflowing neutral gas and the velocity range of this gas. Collisionally excited nebular emission lines are not affected by outflow, and variations may indicate differences in H II region temperatures and metallicities. Higher sensitivity and resolution are needed to fully understand outflow properties and their relation to Lyman continuum escape. The study highlights the importance of understanding LBGs' outflows and their impact on the intergalactic medium. The composite spectra show a wide range of spectral features, including stellar photospheric lines, interstellar absorption, nebular emission, and outflow-related features. The analysis of these features provides insights into the physical conditions of LBGs, including their star-formation histories, metallicity, and outflow dynamics. The study also addresses the potential contribution of AGN to LBG spectra and the abundance ratios of C/O and O/H in LBGs. The results emphasize the need for further observations to clarify the physical processes governing LBGs at high redshift.