The dialogue you are showing in your post is used to define or modify MCE Command inputs, and the actions MC will take as a result of receiving them.
MC already knows all the standard MCE commands and what actions to take. Even though the "Learned trigger code" shows as a ?, the IR commands will work without learning codes. Learning codes simply overrides the default action.
On my system, this functionality has limitations, as MC can only learn MCE Commands, and not any other IR Commands.
Blaster (IR command outputs) functionality is set up in a separate area, accessed by clicking the "Next" button in the bottom right corner of the "Options > Remote Control" dialogue, as per the instructions at the top.
I don't use a Blaster, but the setup for a Blaster should be able to learn commands from any device. i.e. A TV volume up IR code, which is proprietary and specific to the brand and model of TV, should be learnable by MC as a Blaster command, and MC should blast that out to the TV, when the components are set up correctly.
The Wikis could certainly use some work.
