HA will be your "hub". What you need is more like something that lets you communicate to Zigbee devices i.e. a Zigbee dongle. There are a lot of choices and you can search online for the current best option.
HA will act as the main server that connects everything. HA can then expose all of your devices to Google Home and then you can control things via Google Home as well. As an example, if you turned off a light bulb in Google Home the chain of command will look something like this: You issue an off command -> Google Home -> Home Assistant -> Light Bulb.