By default, an html editor is enabled. This allows you to paste or type text into the editor without worrying about adding html code to format it, as the html editor will automatically format your text.
However, if you do not want any html code added to your description, you can turn the html editor off by clicking on the icon shown in the image below.
When it's turned off, you will no longer see the formatting options at the top, such as bold, italics and underline.
Once it has been turned off, you can either paste or type your description. Please do not toggle the html editor back on. If you do that, html code will be added to your description.