User Decision Branching has one input route and two output routes, it will ask user a question, and user's answer will decide which route to go.
After selecting the "User Decision Branching" item from the "Add Flow Control" menu, you will see the editor like this:
You can input the question to ask user. You can also use properties in the question too, just press the button and input property into the question. Below is an example that uses properties in the question.