The hardware they need is the echo dot. After getting the device, they need to install the Alexa App on their phone to set up the device. Within the app, they would add both the echo dot and smart TV device to their acct. That connects the 2 devices.
After that, they can just say "Alexa, open Netflix", or say the movie to play. But if they have trouble switching to Netflix, they will need help setting up the echo dot.