When you need to use some type of formatting, such as for a new headings or making text bold, you do this using wiki syntax or the buttons in the edit toolbar above the editing zone.
Create an underlined Heading: "Equals Signs" create like <nowiki>== References ==</nowiki> creates an H2 heading. See all mediawiki's software markup formatting help here: [https://www.mediawiki.org/wiki/Help:Formatting Format Help]