Restoring IPhone

First of all why do you want to restore?

How do you want to restore? From iCloud or iTunes?

How old is your backup?

If your backup date is D1 and the current date is D2. Then you will lose everything between D1 and D2 unless you take multiple backups for D1 and D2. By default iCloud and iTunes take only one backup per device. In other words, if you take a backup now then the D1 Backup will be overwritten by D2 backup.

Restoring your iPhone will erase all of the data on your phone, and will reset the device back to factory settings. Make sure you complete a backup of your device either to iCloud, or to iTunes. You can find out more about backing up here:

How to backup your iPhone, iPad, and iPod:

https://support.apple.com/en-gb/HT203977

If you backup to iCloud, make 100% sure that you know your Apple ID and password as you will need both to log in and restore your backup.

If you backup to iTunes and choose to encrypt the backup, save the password somewhere safe and do not lose it. You will need this password to restore the backup to your phone, and there is no way to reset or retrieve the password if you forget or lose it.