A list can contain several objects(or no object, or exactly 1 object), hence you cannot directly access a value from a list. If you have exactly 1 object in your list, you can use the list operation Head to get the object from your list; then you can get the value from the object. If you have multiple objects, you might want to use list operation Find. You can learn more about list operations here:
If you want to create a variable of a list you should use a create a list action. Create a variable is for these types.
I don’t understand exactly why you need a variable but you can create a list a do a change list to add the parameter list.
If this doesn’t answer your question please let me know.
Thanks in advance