NOTE: This feature has not yet been added in all the blogs. So, if the tab is currently absent from your dashboard, then do not worry - it will be added soon.
If the tab is already present in your blogs Dashboard, click on it. Now if you have activated "Comment Moderation" in your Blog Settings ( -> Comments), then you will see three sections under the tab "Comments", like this:
NOTE 2: To better manage your blog-comments, moderate them directly from your email.
And if you haven't activated "Comment Moderation" in your blog, then you will see only two options under the tab Comments, viz. Published and Spam.
Now, this "Comments" section not only allows you to manage all your comments from one place, but the "SPAM" sub-section is the main advantage and purpose of adding this new section to the dashboard.
According to Blogger;
Blogger now filters comments that are likely spam comments to a Spam Inbox, much like the spam folder in your email. When someone leaves a comment on your blog, it will be reviewed against our spam detector, and comments that are identified as possible spam will be sent to your blog’s Spam Inbox, found at Comments | Spam.
You can help improve our ability to automatically detect spam comments by checking your Spam Inbox and deleting spam comments and marking real comments that may have been flagged as spam as Not Spam.
NOTE 2: Spam filtering currently only applies to new comments.
So, log in to Blogger and see if you already have the new tab or not. And moreover, you can report any issues with the new spam system by clicking on the “Report spam filtering issues” link on the bottom of the Comments | Spam page, or by visiting this Help Forum page.
Image Credits: Message Defense