Google Home now supports multiple users, allowing up to six unique Google accounts to be registered to a single Google Home unit, along with their respective voice models. The multi-user integration is seamless, meaning that a user does not have to "log in" to the Google Home. After setting up their profile and voice model, they need only speak their command, and Google Home will recognize their voice and apply the action to their own account. Setting up multiple users works mostly the same as setting up a single user, and requires each user to download the Google Home app on their smartphone, link to the Google Home unit, and set up their voice model and preferences.
To set up your profile on a Google Home unit that's in your home, just make sure your phone is on the same network as the Google Home unit, then open up the app. You should find a card that informs you that support for multiple users is available. Give that a tap, and you'll be able to set up your unique voice model and preferences. If you don't see that button upon opening the app, try the icon in the top right that should show you all of your connected devices. As long as you're using the latest version of the Google Home app, clicking on your Google Home in that menu should allow you to start the process of getting everything set up for your own profile on the Google Home in question.
To show off the new functionality, Google created a commercial that shows a family sharing a single Google Home unit just by barking their respective commands at it. The Google Home unit ensures that it's got the right user by addressing them by name, then gives them their relevant information. Presumably, this can extend to things outside of the strict purview of Google services, such as allowing multiple users to shop with their own accounts, or allowing one roommate to call an Uber to get to work right before the other turns on their choice of music. This functionality has been in the works for some time, as evidenced by a recent teardown of the last version of the Google Home app which showed references to multiple users in the app's code.