When you open your Gmail - take a look to see if the side panel is showing (has icons for Calendar, Keep, and Tasks). If it is not showing, look in the bottom right of your screen and select show side panel.
If you would like to create a task with a specific email (in the example below I used a birthday list email) you can simply drag the email into the Tasks icon and create a task directly from the email. You can edit the task and have it set to remind you with a specific date and time.
To make sure it will show in your Google Calendar make sure to select the check-mark next to Tasks under My Calendars.
Embedded below is a 1 minute and 30 second YouTube tutorial.