You define an input variable for the action within the name of the action
Now you can use that variable inside the action body. The string "variable1" will hold the data that is passed on from another action that is connected via a "wire string"
Add multiple input variables by seperating via a comma between them:
myActionName(val1, val2, val3)
If you create a fader/button and route that element towards the action that holds the variable you can now either fill the variable with data (button) or leave it empty for continous fader action: