I am trying to solve a nonlinear coupled partial differential equation using Implicit-explicit (IMEX) schemes in MATLAB, can anyone please provide me some basic tutorials on IMEX method ?

Every study materials and research papers cites this paper: U. M. Ascher, S. J. Ruuth, and B. T. R. Wetton. Implicit-explicit methods for time-dependent partial differential equations. SIAM J. Numerical Analysis, 32:797–823, 1995. But I am not able to clearly understand the logic behind this IMEX method.