The iTunes way: How to Back Up on iTunes
1: Connect your iPhone to your PC (Mac or Windows) via an USB cable. Then launch iTunes.
2. Select your iPhone in the ‘DEVICES’ list and Right-Click on your iPhone
3. Then you will get a drop-down menu, select the “Back up” option to start back up your iPhone to this computer.
4. Wait till iPhone backup is complete patiently. That’s all
The iCloud way: How to Back Up an iPhone to iCloud
1: Make sure your iPhone is on a good wireless network (Wi-Fi), a good network is important for you to make a good iPhone copy.
2: Connect the iPhone to a power source and open the Settings app, select iCloud, and tap Storage & Backup on your iPhone
3: Scroll to the bottom of the screen and tap on Back Up Now. Then just wait patiently