place you cursor where the description filed should go, the go to WebAssist -> Forms -> HTML Editor -> Insert Editor to add the html editor instance.
by default, the editor name option will be set to editorField, you can change that to description.
in the bindings panel, a new element will be added to the form collection for the HTML Editor instance that was added.
in the insert record behavior, bind the description database column to the form element for the html editor instance.