From Pages or any web page (called “posts”) generated with WordPress?
To remove the comments from a single post, in the Write Post panel of the Administration Panels, uncheck the box that says “Comments” near the title.
To remove comments and sidebar from your entire site, well, that’s much more complicated. If you remove the instructions in the core template files (index.php, single.php, page.php, etc.), you will have an empty space in your Theme‘s design. That requires familiarity with CSS to redesign the theme. You can also look for a Theme that has no sidebar and just go that way.
If you want the sidebar removed from just one particular post, well, that requires a query with Conditional Tags that basically says “If post number 17, don’t show the sidebar” and every post on your site will pass through that query.
So a little more information would help.