When to moderate or blacklist a comment

If you scroll down the page a bit, you'll see the Comment Moderation area:

This is an extension of the moderation settings from the top of the page. Note that if you've checked the Comment must be manually approved checkbox, you can safely ignore this Comment Moderation box. Otherwise, you can use this box to help WordPress figure out which comments are probably okay, and which might be spam or inappropriate for your blog. You can tell WordPress to suspect a comment if it has more than a certain number of links, as spam comments are frequently just a list of URLs.

The larger box is for you to enter suspect words and IP addresses:

• Here, you can type words that are commonly found in spam (you can figure this out by looking through your junk email), or just uncouth words in general.
• The IP addresses would be those of any comments you got in the past from someone who commented inappropriately or added actual spam. Whenever WordPress receives a comment on your blog, it captures the IP address for you so that you'll have them handy.

Scroll down a bit more, and you'll see the Comment Blacklist box:

Unlike the Comment Moderation box we just saw, which tells WordPress how to identify suspect comments, the Comment Blacklist box tells WordPress how to identify comments that are almost definitely bad. These comments won't be added to the moderation queue, and you won't get an email about them; they'll be marked as spam right away.