Reminders aren't the same as regular calender events, and they operate quite differently in Google too. For example they might not be tied to a certain time or could be dependent on you being in a particular place. To date, Google has kept reminders and regular calendar entries apart, but that's all about to change.
This week, Reminders are being added to the Calendar app on Android and iOS and to the desktop version. You'll be able to add a reminder straight from the app itself and it will pop up in your feed for the day. But it will also work in a unique way, with your to do list staying with you throughout the day until you engage with it and tick off the items that you have completed.
If you don't manage to get it done, that task will be back the next day and will be a part of the events you have planned. You'll be able to add these new reminders from a number of different apps, even while writing an email which was something we were just thinking would be useful last week.
It sounds like a great addition to what Google offers, and you can also add reminders just by saying 'Ok Google'.