If you aren’t signed into Reddit, make sure you sign in before attempting to leave a comment: click log in in the top-right corner of the page, then enter your username and password.
If you want to quote the original post’s content, you’ll find it at the top of the thread.
If you want to reply to a comment, you’ll first click Reply below the comment.
If you’re replying to a comment, you’ll instead click REPLY below the text box.
