Consider a system of three harmonic oscillators (SHOs), each with possible energies 0, 1ε, 2ε, 3ε, ... If you are given the total energy, then you know that the sum of all the oscillators' energies is equal to the total energy. One way to compute how many microstates there are is to write down how many states there are if the first oscillator has 0, 1, 2, and 3 ϵ energy, then sum them all together.