Signed-in members can comment on blog posts and reply to other comments. You can edit a comment for 15 minutes after posting it, and delete your own comments at any time. Replies to your posts and comments show on your Activity page.
If a comment breaks the guidelines, report it and staff will take a look.
On your own blog, you're in charge: you can remove comments on your posts, close comments on a post, and block members from commenting on your blog.