Transition metal oxides exhibit strong correlations due to their open d shells, influencing magnetism, doping, and strain effects. Using many-body methods like GW Approximation and DMFT in conjunction with DFT, we investigate these effects in perovskite and layered oxides which are of significant technological interest, taking the example of prototypical materials like LaMnO3, SrTiO3 (perovskites) and LiMnO2, LiNiO2 and LiNiaMnbCocO2 (layered oxides). For perovskite LaMnO₃, a colossal magnetoresistance oxide, Jahn-Teller distortions lead to an antiferromagnetic insulating ground state, but in LaMnO₃/SrTiO₃ heterostructures, a ferromagnetic insulating state emerges without an explanation. We demonstrate that strain stabilizes ferromagnetism absent in bulk LaMnO₃, and the insulating state arises due to correlation effects, thus elucidating the interplay of strain and correlation in tuning magnetism. Moving onto layered cathode materials in LiMnO₂, de-lithiation i.e. Li-doping induces exotic correlated metals with mixed Mn³⁺/Mn⁴⁺ oxidation states due to polaronic quasiparticles, leading to doping-dependent phase transitions. Finally we investigate LiNiO₂ which has the highest capacity among layered Li-ion cathodes where DMFT reveals a mixed Mott-charge-transfer gap and ligand-hole states, explaining its suppressed Jahn-Teller distortion and enhancement of O redox behavior. Doping LiNiO2 with TM like Mn and Co forms Ni-rich LiNiaMnbCocO₂ (NMC) cathodes, where charge transfer creates ligand holes on O in Ni-rich regions and ionic behaviour in Ni-poor regions, leading to dual redox of O, influencing redox reactions.