This is an important part of posting, as it preserves the flow of the conversation, and makes it easier to allow others to joinin the discussion. FreeRepublic does include a great feature that allows you to see the original post, but including the reply in your post is a Good Thing®.
Nothing is quite so hard on the eyes as long posts that are essentially one huge paragraph. Break those paragraphs up! Use the paragraph tag <p> to create new paragraphs (this will automatically add a blank line above it, which helps to create the separate paragraph).
Another HTML tag used in formatting posts is the <br> tag. This is equivalent to hitting the return key, in that it starts a new line of text. Two of them together equal one paragraph tag.