How to use the "Custom decision" and "decesion activity" ?

Hello there

Thanks for all what you're doing in this community, I got so much help here to use vCO.

I am trying to create some workflow that based in the decision of the user it calls another workflow. In other words the user has to chose between two choices (= two workflows to run).

Here is picture that shows what I am trying to do.

If the user said "Linux" for example, it is gonna be the workflow of "create linux VMs with single nic from template" that would be run, if the user said windows it is gonna be the other workflow that would be run.

So my questions are :

Is there any other method more simple ?

How can I use the "custom decision" so that the user had to answer a question before starting to fill the parameters of the workflows ? what should it have in the "in parameters" ?

Thanks!