Click any text to edit or style it. Click blue "Gear" icon in the top right corner to hide/show buttons, text, title and change the block background.
Click red "+" in the bottom right corner to add a new block. Use the top left menu to create new pages, sites and add extensions.
Google has a highly exhaustive list of fonts compiled into its web font platform and Mobirise makes it easy for you to use them on your website easily and freely.