Quiver Hecke algebra is a generalization of the affine Hecke algebra from the point of view of categorificaiton of a half of the quantum group. In this lecture, we will review some basic properties on quiver Hecke algebras. We will study the finite dimensional graded representations of quiver Hecke algebras. The notions of characters and convolution products will be reviewed; the categorification theorems will be presented without proof.