Your reminder will appear on your phone when you arrive at the given location. If you say, "remind me to grab some cereal from the grocery store," then you'll be notified when you get to a grocery store. We confirmed the feature by asking home to remind us to get coffee beans the next time we were at Starbucks (don't judge). Home replied, "Sure, I'll remind you on your phone the next time you're at a Starbucks," which sounds like Assistant will remind us at any Starbucks we end up at. That's in contrast to asking Siri to remind you, as it asks which Starbucks you want to be reminded at. We've reached out to Google for more details and will update this post if we hear back.