The comments panel allows you to manage the comments you receive on your website. WordPress.com has a built in spam filter so you shouldn’t receive very many spam comments at all. If you do, you can mark the comment as spam, much like you would an email.
Depending on your discussion settings, you can opt to have comments automatically displayed on your posts and pages or you may have chosen to moderate them via the Comments panel. Whenever someone comments on your site, the site owner will receive an email notifying them of the comment and providing them with quick links to moderate the comment.
Note that depending on the theme you have chosen, you may not have the option to allow comments on pages. Some themes only provide the facility for comments on posts.