The navigation links are created when you create a new page in your site - it automatically updates.
To create a button, in the text editor highlight the text you want to be a button. Link that text to either a page or external url (either by clicking the Add a Link to a Page link or the link icon) then with the text still highlighted, select button from the Styles dropdown toward the top of the editor.

Hi C5mix,

I tried clicking on the Style drop down menu as you advised but there is no dropdown menu. There is only the dropdown for the Format, Font size and Font family but not for Style.
Is there another way of adding a button?

Thanks!

That doesn't make sense. There should be if the theme was installed correctly.

You can also just do it within the HTML by adding

to the <a> tag