The web works, internally, using a formatting system called HTML. We assume that you do not know HTML and do not want to learn; when we process your Description and Note information, we turn it into HTML for you. Mostly that means that we turn blank lines into new paragraphs.
But: if we find any HTML at all in the information that you have provided, then we don't do any converting. We remove the HTML codes that would conflict with our server, and leave the rest alone.
There is no middle ground here: you can't have automatic formatting of some parts of your advert and HTML formatting of other parts.
Here are the HTML tags that we can handle, with a short summary of what they mean. If you do not already know HTML, this is probably not the right time to learn. If you have to rely on the format of your advertisement to attract attention, there is probably something wrong with its content. But if you do want to learn, we recommend this introduction as the best place to start. Remember that your advertisement will be one piece of a page, and all such introductions assume that you are producing the entire page, so pay no attention for now to things like page titles.