Fitting curves in Jupyter Notebook without using the fit function [closed]

For a task for school, I have to write my own fit function by using the least squares method. The problem is I don't know how to do that, specifically I don't know how to minimize my function to calculate my fit parameters.The problem here is also that my fit function is not linear, so my book says I have to try guess some values for my fit parameters and then minimize my function. But still I don't know how do to that. The code that you can find below is my code right now, I got it from somebody but I don't understand what it does so :).

def fit(x,mu,gamma,back,A):