Summary of Blog posts

Going around in circles here. We have a new website up and running and part of what we want to do is create regular blog posts. We have added a Blog menu option to the main navigation bar and which points to any posts that are categorized as Blog posts. However, the posts are displaying in full and we want to condense this to just the summaries for two reasons - firstly for space and aesthetics, but also for the ability to share the blog (facebook/twitter etc). The sharing buttons only appear if you have clicked into the blog post but not if you just click the blog menu option. i have made the necessary adjustments to the reading options however, as the blog menu button does not point to a page, we do not have the ability to select "blog" as the Posts Page in the reading settings. I suspect this is the issue. Is there anyway to force the blog roll to condense blog posts to summaries with the set up we currently have? The alternative, I figure, is that we have create a page called Blog which we then assign as the posts page. I'm not sure whether this would operate in the way we originally envisioned but is it the only way to achieve the summaries? our site http://www.5for5challenge.com/category/blog/ - any help/suggestion greatly appreciated!