jlet explained in #5 what they are.
Discrete commands are separate commands, one for each of the input sockets on your TV, that you can use individually instead of cycling through the list.
I said in #7 that the Harmony database DOES have them for your device.
They don't appear on your original remote but they have been provided as a bonus for use on Harmonys.
In the software go to Devices> TV> Settings> Customise Buttons, press one of the down-arrows under Commands and you will see that the drop-down list includes commands with names beginning with Input.
You should test those that you need, then if they work use method 2 to set them.