Adding reminders to Google Assistant is as simple as saying "Hey Google, remind me to..." to your phone or smart speaker. You can also use the Calendar app or website to create reminders, do a Google search for "remind me" on your phone or computer then fill the details, or use the Google Search app and head to the Reminders section. If all of these methods weren't enough for you, there's a new one now.
In Assistant's Snapshot (the inbox-like icon when you activate Assistant), you can see a new floating action button on the bottom right. Tapping that Google-colored plus reveals only one possible action: adding a reminder.
On my Pixel 4, there's a pause of a second, then Assistant's reminder creation card pops up. The mic doesn't get activated, so you can't dictate the reminder, but that makes sense. Since you've already opened Snapshot, tapped the FAB and the reminder icon, the phone is already in your hand and typing fits better with that workflow. Plus, there are already plenty of ways to add a reminder by voice, so it's good to have one where you don't need to speak for those situations where you can't talk aloud.
Once the reminder is created, it shows up in your Assistant Snapshot, your Google calendar, and the reminders section in the Google Search app, as usual.
The new FAB is rolling our server-side, so if you don't have it yet, all you can do is be patient and hope you get it soon.