A personal identification number, or PIN, is a set numbers used to prove the identity of the user for a service or device. A passcode is very similar to a traditional password. You can think of a passcode as a PIN with letters, symbols, and numbers. You will use this PIN/Passcode to access your device and any apps that require it.

Your device will, most likely, be using a default PIN. For security reasons, it is highly recommended that you change this as soon as possible.

1. Go to your Settings app
2. On the left side, scroll down until you see Touch ID & Passcode. Tap to open.
3. A popup will appear. Enter your old PIN.
4. After that it will ask you to "Enter your new passcode." Make sure it's at least 6 digits long, or it will popup saying your passcode could be easily guessed. If you wish, you can also use letters and symbols by tapping on Passcode Options, then Custom Alphanumeric Code.
5. Repeat your PIN/Passcode to complete the process.