Let's look at making a simple trigger. Say we want to detect when we are getting thirsty, and automatically drink something. The most reliable way of making a trigger is to wait for the message to appear:
Now, Shift+Double-click to select the entire matching line:
Press Ctrl+C to copy that line to the Clipboard, and then press Alt+Enter to open the world configuration dialog, select Triggers, and click on Add. (Pressing Shift+Ctrl+8 also opens the world configuration and takes you directly to the triggers list).
Paste the message we want to match on into the Trigger box. Type in what to do when we are thirsty into the Send box (you can make multiple lines if necessary).
That is all you need to do. Click OK to close the trigger dialog, and Close to close the world configuration dialog.
We can do more, though. Perhaps it would help to colour the matching line in a more distinctive colour. Whilst editing the trigger we can choose one of the custom colours from the drop-down list, or choose "Other" colour, and then click on the two colour swatches to make any foreground and background colour.
It might help to have an audible notification. If you want one, click on the Sound "Browse" button, and choose a suitable sound. There are thousands of sounds available over the Internet, or on CDROMs you can purchase in shops:
Once you have chosen a sound its name is shown in the main trigger window. You can click the Test button to make sure that you have chosen the sound you want.
You can always go back to the trigger list, find the trigger you want to change, and amend the way it behaves.