First, take a deep breath. Don't panic.
Make a note of the time and date of the accident - use the Notes app on your phone, a pen and paper, or record a voice message. Take pictures of the accident, including of your car, the other car, and the scene in general.
Get the other driver's information, including their name, phone number and email address, car registration details, insurance information (including provider, insurance number, and policy details), and their driver's licence number. When you're speaking with the other driver, don't admit fault. Give the other driver your details as well.
If there are witnesses, get their details and their accounts of what happened. If there's some kind of dispute, their accounts of the event could be helpful.
Then call the police and report the accident, and call your insurance provider. :smiley: