Actions on User Update

Actions on User Update


Hi there,
 
I am trying to see if I can get a better explanation of this feature.
 
I am completing something for my school.. If a student checks the box next to "9" on grade.. that being my if field,
 
I want another question to appear saying, please select homeroom teacher.. then list my 7 9th grade homeroom teachers.
 
and so on for grades 10, 11 and 12. 
 
Am I using the right feature and can some body please provide some guidance.
 
Thanks