llilly on "do posts on blog page function as page? ie read more tag"

I have tried all the ways to add the read more tag on my posts...shown to be as simple as pressing the tag button on the post text etc. But it never 'takes' when my post is shown on the blog page. I'm beginning to think this is due to the fact that my posts are contained in the 'blog' page on my menu and pages don't respond to the read more tag...
I do not want to go into my php/css files on this especially as it should be 'easy'...any way to have a designated 'blog' page on the menu and have it function as a blog post?
Thanks