To get started, add a new chapter using the + button just below your document title. You can now click the Chapter button left to your new chapter title.
In the Chapter options window, click the tab Numbering and choose None.
In the Advanced tab under placement, click Front. If needed, select break before and after to get the chapter onto its own page.
When you confirm your changes and export with a thesis template, the new chapter will be placed into the preface of your thesis document.