Hi, 
I have two questions about my blog:
1). How can I get summary text for my blog to appear 
here?
2). After adding the 'Archives' widget to 'Blog sidebar', I've found that rather than displaying only what was published in a certain month, ALL blogs I've ever published are shown, including one of them twice (see 
here, for example). How can I correct this?
                  
                
Comments
1. Wordpress creates content in this place in 2 different ways:
- automatically, based on content in WP editor (you can use Builder >> SEO option and "Hide the content")
- you can use Excerpt field which is under the post edition. Or if you don't have it there, you need to activate it in the right top corner where Screen Options is.
2. You probably did not created Blog page properly. We suggest to look at http://themes.muffingroup.com/betheme/documentation/#blog where we described how to create blog page properly.
#Filters .filters_buttons li:not(.tags) { display: none !important; }4. Where can we find those comments on your site?5. Looks like date is missing because you use different template than Default Template. Templates for posts are set under Post Options > Layout section.
.Recent_posts ul li .photo .c { display: none !important; }5. But what kind of template for single post pages you set?