I'm not sure what you are looking for here. You are posting
in the RoboHelp HTML forum, so I would assume you would probably be
using Style Sheets to govern your look and feel. Normal is the base
font for all your body text.
Place focus on some normal text the WYSIWYG editor and click
Format > Styles...
Now click the Modify... button
Click Format > Font...
Select your font and size as desired
Click OK until all dialogs are gone