It is recommended that you create a separate content type for user submission forms if only users will be submitting the form. However, if both administrators and users will be submitting content, use an existing content type. Whether you are creating a new content type or using an existing content type, you must edit the Author Entry form to include all the fields that you will need for the Create Content forms. If you add a field to a Create Content form that is not in the Author Entry form, the data submitted by constituents for that field will not be collected.
Warning: Be careful when editing Content Types after you have added Create Content forms to a web page. Certain changes can invalidate the form. Furthermore, if the page with the form is unpublished, when you publish it, any submissions made with that form will not create a content type.