Google Now kept track of parking locations before, but it wasn't with any degree of accuracy. The latest version of the Android Google Maps app circumvents how inaccurate the feature was by having you mark a parking spot for yourself. That's a pretty stark comparison to the dark magic (read: GPS and other data) that Now used prior.
Simply open the application after parking, tap the blue location dot and you're good to go. From there you can add notes (helpful for jotting down location in parking ramps) and even take photos to remind you which blue Toyota Camry is yours. Additionally you can add a timer so you know when the meter will expire. All of this info can be pulled for notifications and alerts, too.
As Android Police points out, though, this appears to only work for one car at a time. Not a huge deal, but it does rule out keeping track of your car at home, and a rental car in another city while on vacation.AP also notes that some Android Auto users might see a new arrival screen too. Oh, and folks using Maps to find their way around via public transit could see weather alerts.