An example would be, "Hey Google, remind me to pick up milk when I'm at the store".
In the case of "Good Morning", which seems to be the first of the multi-step routines to go live, you can get Assistant to do stuff like turn on your lights, tell you about your calendar or the weather and traffic, and then pop on some tunes or a podcast all with a single command.
What's new here isn't so much location-based reminders, of course, but the ability to set them on one device and have them appear on another. You can set one time reminders and recurring ones as well. The routines can be set up for one person, or more than one person, to use through Google Home devices. Now, if you have your hands full at home, you can do all that through a smart speaker entirely by voice. You can set Assistant up to read you your unread texts; send texts; get commute info, broadcast to Google speakers at home that you're on your way back and adjust smart home devices ready for when you return. It will be able to control your smart home devices that are connected to your Assistant and retrieve information for you when you need it. Needless to say, you will need to have location services enabled on your smartphone for the notification to trigger.
These routines will also change depending on who's talking to the Google Home, so if you have loaded your profile it will give calendar alerts specific to your account. Instead, the Google Home asked when I wanted the full instruction to be issued as a regular reminder.
A location-based reminder is triggered, as the name indicates when you're at a certain location. Saying "Ok Google, remind me to check tire pressure at the gas station", by example, wasn't understood in terms of the gas station being a location.
That's all likely to improve as time goes on, and as the Assistant learns to differentiate more accurately.