Look at the box in Odin. It should turn blue or light blue, indicating your phone is successfully connected. Click on the AP button in Odin. Browse and select the downloaded TWRP recovery .tar file. Click on the Options tab on the left side of Odin.
Go to the "Options" tab in Odin and uncheck Auto Reboot . This ensures that the custom recovery is not overwritten by the stock system upon reboot. Click the Start button to initiate the flashing process. twrp samsung j2 core
Connect the phone to the computer. Odin should display "Added!" and a blue/light blue COM port. Look at the box in Odin
The Samsung Galaxy J2 Core (launched with Android Oreo/Go Edition) has a locked bootloader. You cannot flash TWRP without unlocking it first. Browse and select the downloaded TWRP recovery
Since you disabled Auto Reboot, your phone will remain stuck on the Download Mode screen.