How to back up my apps on itune?

I want to factory reset my Iphone then restore all apps again, how to back up and restore apps from my computer?

If you look on the app icon on your phone now and hit purchased all your apps will show, they are on iTunes and don't get deleted. So when you finish restoring your phone, you go to apps-purchased and hit the cloud pic icon and they will be restored to your phone.

How to back up
iTunes can create backups of your iOS device when you:

Sync with iTunes (disabled if you have iCloud backup turned on)
Right-click (or Control-click) the iOS device in iTunes under Devices and choose Back Up
Use these steps to manually back up your iOS device using iTunes:

Connect your iOS device to a computer with the latest version of iTunes installed.
Click the File menu and select Devices > Back up.
To verify that the backup finished successfully, open iTunes Preferences and select the Devices tab. The name of the device will appear along with the date and time the backup was created.

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