Selecting post categories for blog page

I can't seem to see that this question has been answered before, but if it has I apologise. I am trying to set up a new page using the blog template, but there doesn't seem to be anywhere to specify what post category I would like displayed on the page. I have a couple of pages using the blog template, but need different post categories shown on each page. This is probably something really easy, but I can't seem to find where this is set up. Can you please help? Thanks in advance.