Check out the NEW GMAIL by clicking on the Settings gear and choosing "Try the new Mail". You're going to like it!
When you open Calendar from Gmail, you can see items on your calendar and create appointments. Also, when you open Keep from Gmail, if you have an email open and take a note, the Keep note will be linked to the email. (If you aren't using Keep right now, you should start! There's much more that you can do with Keep and it all works with Google and on your phone!) Finally, when you open Tasks from Gmail, you can add Tasks and check off Tasks that you've completed.
