From the lead record or the post-call follow-up, click Create a task.
Choose the appropriate task type.
Set the date and time when you want to handle it.
Add a short note with useful context.
Click Save.

The task is assigned to you and automatically joins Overdue, Today, or Later based on its due date.
A task remains linked to the relevant lead. The Call back button on a missed-call notification starts a call immediately; it does not create a task.