To select a font for your presentation, just look for the Font button located in the upper part of the editor screen. Scroll down the fonts panel to find a selection of premium fonts available for everyone. 

Select the font you'd like to use. Once you click on it, a little menu window will pop-up asking you whether you'd like this font to be applied to the Headings, the Body text (paragraphs, charts, captions, bullets) or all the text of the presentation. 

Premium subscribers can use their own fonts. To add your own font, go to the Font options and click on the "+ New Font" button, to be able to upload the font files.