To exclude a category from the ‘More posts’ section you need to modify the query by which it’s being formed in single.php (the $args array around line 62). Here are the possible category parameters described in the Codex.
So, for instance, to exclude a category with the id of 20 you would do the following:
Yeah, that works pretty good. Thank you very much.
I have one more question. When I added your template (demo content) i got homepage with shortcodes (i think occurs to layout i choose> 2 columns or 3 columns grid…). But I removed them. Is there anywhere where I can find all shortcodes I can use to build home page or it is a fixed layout, if you understand me?
As for the shortcodes, there are no shortcodes created by this theme. What you saw might have been the [gallery] shortcode (which comes with WordPress) or shortcodes created in your content by a previous theme.