We will survey some results of stated $SL_n$ skein algebras and show how to use them to study the ordinary skein algebras of surfaces. We will discuss the integrality of the skein algebra, the injectivity of the cutting homomorphism, and the structure of the skein algebras of the bigon and the triangle. The talk is based on joint work with F. Costantino, J. Korinman, A. Sikora, and T. Yu.