To import a private key you must first have a wallet created with a 12 word seed phrase. When you start your TronWallet app after a brief introductory start screen you have two options to continue with your TronWallet experience: create or restore a wallet. If you do not yet have a 12 word seed select create and write the 12 word seed down (keep in a safe place). After doing this you in your wallet in the top right you will see a + sign. When you press it it will go to the add accounts screen. Select IMPORT /W SECRET KEY.
Enter your PRIVATE KEY in the box labelled secret key. Your private key consists of 64 characters. Copy the private key of the account you wish to import and use the paste icon to enter it. It will auto generate your address. Once you have done this tap CREATE and confirm pin.
If you do this successfully you will be redirected to the main screen where you can resume your activities within the app using your imported wallet. You can add multiple wallets with private key using the +

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