Enabling or disabling comments in WordPress can quickly be done site-wide or on a per-page or per-post basis.
To change the comment settings site-wide, go into Settings > Discussion.
To enable or disable comments on a per-page or per-post basis you first need to be be editing the page or post. Then, go into the Screen Options tab (upper-right) and check the box for Discussion.
The Discussion box will appear (typically under the main post editor) and you can control whether to allow comments and trackbacks on that specific page or post.