Setting Properties 
The application supplies a context and processes the function using a mode of operation.
Under the Detail section, under the Properties tab, choose the mode of operation in the Mode field.
There are three modes of operation:
Functional mode
Event mode
Functional and Event mode
Note
If you choose Functional Mode or Functional and Event Mode, a top expression has to be assigned to the function.
In the Event mode, you do not need to assign a top expression to the function.
More information: Modes of Operation
Enter the context class.
Choose the trace mode.
More information: Tracing Functions