If you want to reply specifically to another user's post, use the 'Reply' link at the bottom right of the post. This will start a new post with that user’s post quoted. You can then add any additional information you want and submit your reply. You can also highlight any part of another user’s post and a small pop up box with the word ‘Reply’ will appear. This gives you the ability to quote the highlighted part of the post. Click ‘Reply’ and you’ll see that section quoted in the text box.