You insert equations much the same way you insert page breaks, tabs, and other stuff. And from the same keyboard menu. It brings up an equation editor, where you can enter either LaTex or MathML code.
From what I've read it's better to use an app that specializes in creating the equations, then copy/pasting them into the equation editor in Pages (not directly onto the page). The app I've heard recommended is Myscript MathPad, which lets you enter the equation by hand (using the Apple Pencil), then coverts it to to LaTeX or MathML.
In my screenshot below, I used the Apple Pencil to create an equation in Nebo to do the same thing. It kind of suprised me when it worked, since Nebo doesnt' mention that it's equation mode convets to LaTeX.
In my quick experiments I could change the size and color of the equation, but nothing else.
Note: I'm using a hardware keyboard, which is why you only see the keyboard's shortcut bar at the bottom of the screen. Hirango Sans is not the equation's font. It's just the font I tried to change the equation to when experimenting.