What is the `pm.Metropolis`standard deviation parameter?

I am looking at the different parameters of the Metropolis step method. After reading the documentation, I don’t quite undestand what is the S parameter. It is supposed to be Some measure of variance to parameterize proposal distribution, but how is it used by the sampler? Is it used to initialize the standard deviation of the proposal distribution? If so, how can I pass different values for my different parameters?