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If you can access internet on your iPhone, then you are connected to WiFi network. If not, then have to connect to it.
On your iPhone, open Settings app. Tap WiFi option and you will see your WiFi networks there. Tap your WiFi network and enter your WiFi password. If you don't remember your WiFi password, check the bottom or back of your router and it should be there, mentioned as WPA Kep, WEP key, Passphrase etc
Once you are connected to WiFi, go to Settings tap iCloud. Tap Backup and tap Backup Now button and this will backup your iPhone.
If you have any questions or would like any additional information, please don't hesitate to ask.
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