How to debug code in Toad?

e.g.
Toad for Oracle -> Database -> Schema Browser -> Click HR -> Click Procedures -> Double click to "PROC_EXEC" procedure -> Set breakpoint or Add Watch (optional) -> Press Shift+F7 or Click Debug-Trace Into -> Confirm -> Click Execute

How to use "Toad for Oracle" Help?

e.g.
Toad for Oracle -> Help -> Contents -> Search "Debugging a Procedure or Function Tutorial"

How to enable debug mode?

SQL> GRANT DEBUG CONNECT SESSION TO hr;
SQL> GRANT DEBUG ANY PROCEDURE TO hr;

Lastly, reconnect to the session and try again :)