Nakajima quiver varieties appear in various fields, including symplectic resolutions, instanton moduli spaces, and representation theory. In this talk, I will introduce the basic notions of quiver representations and outline the construction of quiver varieties using Geometric Invariant Theory (GIT). Following this, I will explain how to construct highest-weight representations of Kac-Moody algebras via the convolution product on the Borel-Moore homology of Lagrangian subvarieties, illustrated with a tractable example.