Scenarios are complete packages of one use case of Simon.
For example: If you want to control Firefox, just install the Firefox scenario.
Scenarios include your vocabulary, grammar, trainings texts and commands.
You can download and import scenarios through the manage scenarios dialog (Manage scenarios > Import > Download). You can also browse this repository online.
If you create new scenarios, please upload them through the upload feature from within Simon or directly on KDE Files (see above) to share them with other Simon users.
Next to scenarios, you need to train / create / get an acoustic model before Simon will recognize your voice. You might want to look at base models for more information.