How do I include an f(x) equation in MATLAB that still evaluates with using iterations?

I am newest to MATLAB, suppose I have f(x)=x^3+8x-1 and I want to solve for the root using the iterations. I want the user just to open my script and the user will find the answer. I already did the code for the iterations, I just dont know how to include a function equation within the code. Also, the f(x) is used in the iterations, so the value of x changes.