Getting widgets to appear only on blog page

I’m using the Mantra theme. I’ve set the home page to static and the blog page as the blog and I’ve tried setting the template to both blog and default. As soon as I put widgets (Archive, Previous comments etc) on the blog page, they appear on all the pages.

I’ve looked up the help files and see there’s a line is_page() but, typical of IT manuals, it doesn’t tell a non-programmer like me what to do with the code!!!!!!

I’d be grateful for some explicit advice on this please.