While you've writing your script, you're probably going to want to test it, to see how it flows in practice, and make sure any conditional logic behaves as you expect.
While you can of course run dialogue in your game, a quicker and more convenient way of testing before you get to that stage is to use the in-editor dialogue testing feature.
To open the editor runner, you only need to double-click a SUDS Script Asset. The window has a few areas:
The toolbar is where you can find the "Start Dialogue" button. This (re)starts the dialogue from the label shown in the drop-down box to the right of it.
This defaults to starting the dialogue from the beginning, but you can start from any label defined in the script. This can be handy if you use combined scripts for lots of smaller interactions and just start the dialogue from the appropriate section, rather than having lots of separate scripts.
Once the dialogue is running, you'll see speaker lines displayed in the Dialogue Output tab. Buttons will appear at the bottom of this tab for you to make choices, or simply continue the dialogue.
The trace log at the bottom shows everything the dialogue output window does, plus additional information about which line is being executed, what changes are being made to variables, and what conditional lines are evaluated and what the outcome was. The trace log is very useful for debugging what's happening in your dialogue.
The variables tab shows the current variable state for the dialogue. It's editable, so you can change any variable values on the fly if you want, to simulate different scenarios.
Variables which are set in the script appear here automatically, but you can also manually add variables as well. This is usually variables which would be supplied by code while the game is running, but you can hack them in here for testing.
Any variables you add manually will have a slightly purple colour tint:
Variables you manually add will not be cleared when you restart the dialogue, unlike the rest of dialogue state. This is so you can re-run the dialogue multiple times and not have to keep manually setting up the state every time.