A list of sans-serif fonts will load.
Find one you like, click it.
Info regarding the font you clicked will display, a list of characteristics.
Found the sans you like?
Click the PLUS.
You can click on the serif fonts for more info too. Only fonts with matching x-heights will be displayed. Fonts in black have significantly different contrast than your sans, the ones in red may be too similar.
Click the download link to download a font.
You can always go back into the sans list and pick a different font, the process will start over.