This lecture covers topics such as the effective field, Landau-Lifshitz equation, magnetostatic modes, spin waves, the Holstein-Primakov transformation, Kittel formula, demagnetization field, Polder tensor, Walker modes, long wavelength limit, and exchange spin waves. It also delves into the concept of one-magnon eigenstate and the Holstein-Primakov transformation, discussing eigenstates of Szi and long-range interactions. The presentation concludes with insights into spin wave dispersions in thin films with or without DMI interaction.