There are two options. If you pair directly to google home, you have to control it like you would any other light. You dim to 25% for low, 50% for Medium-low, 75% for medium and 100% for high. If that works for you, then you are all done at this point.
However, I didn't really like that method, so I came up with something much, MUCH more involved using IFTTT that allows me to speak the speed name to Google Home. This uses the maker API in HE and IFTTT to get it to work. if you want more details, I can provide them. But if you're not used to IFTTT, then this wouldn't be where you'd want to start as it is pretty involved. The dimmer option would be easiest.
Also, I would advice making a separate room in Google home for "Fans". In Google home they will show up as lights. So, when you say shut off the lights for the room, the fan will shut off as well. You may also want to edit the device names before pairing to google home. For example, in my office, the main unit, which is not paired to anything is "Office Fan Main Unit" . The fan is named "Office Fan" and the Light is called "Office Fan Light". Otherwise you end up with "Office Fan Fan" and "Office Fan Light". You can edit the label applied to the device on the edit device page.