We get the parameters of the intercept from the posterior distribution? The single value that is indicated as the intercept is how exactly related to this posterior distribution…or how do we come to that.
Is the posterior distribution different for each variable for a ‘model a’? for does the whole model has a single posterior distribution for all of its parameters?

I was trying to explain Bayesian to my roommate and actually understood I don’t really know these basics…

I don’t think this forum is the right place for very basic questions like these. There are many very good introductory resources available online (blog posts, YouTube lectures) that may be more useful to improve your conceptual understanding of Bayesian data analysis - probably just a Google search away.

@aldc Do you have a particular example that you can share? Are you talking about the intercept from a model you fit with Stan (e.g., via rstan, brms, rstanarm, etc.) or just Bayesian stats in general? Like @erognli said, you will probably find many more introductory resources elsewhere online, but if you have a model you fit and you have questions about the interpretation of that model then you can definitely ask about that here.