Often, the title page is set up in the template to have content on it automatically. This content might could be a client name, a date, or an image. If this is the case for the layout template you are using, you might be unable to add any content in the Title Page section of your document without it overlapping the content added by the template.
If you would like to have a section that occurs before the rest of your document, such as a cover letter, create a new section and arrange it to be the first section of your document. This section will appear at the beginning of the document, but keep in mind it will still appear after the title page and Table of Contents.