the same thing you're just saying I pretend I already saw a few experiments I have pseudo counts for those pretend experiments and I multiply the probability of those into the likelihood of the actual experiments do the same thing for a Gaussian to make the math work out you want the prior for your mean of your Gaussian they also be a Gaussian because then you have a Gaussian multiplied with a Gaussian and we know that's again a Gaussian and the math will be easy if you said well actually I think the prior for the mean