Some apps and system settings allow you to launch an application in specific situations. For example, the Bixby feature on Samsung devices lets you open an app with a double-press of the power button.
For these situations, you can install one of the Tasker Extra Trigger apps. These are small, simple apps with no user interface; their only purpose is to trigger this event in Tasker when they are opened.
In the Bixby example, you would assign one of the "Extra Trigger" apps to the double-press of the Power button. When you perform that action, the selected trigger app will launch, which will in turn activate this "Extra Trigger" event and run your corresponding task in Tasker.