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You must know the router password *****
Open or tap Menu→Settings
From the same screen, tap Wi-Fi Networks.
If Wi-Fi is not turned on, you will get a message asking if it should be turned on. Tap OK.
Or, if the Kindle Paperwhite is in Airplane mode (that is, Wi-Fi is not turned on), you'll see a message asking if you want to turn off Airplane mode.
Select the network to which you want to connect, you need to enter the router password.