i made a ComboBox with Primary, Junior & Superior what i need help with is code for if i select Primary in ComboBox it will select ListBox1 if i select Junior in ComboBox it will select ListBox2 and Superior in ComboBox it will select ListBox3
Detecting that an item has been selected in a ComboBox and which item it is will be the same no matter what you want to do about it. Populating a ListBox with items will be the same no matter when you want to do it. Two simple problems to solve and then just put the solutions together.
That said, if the data is coming from related tables in a database, you could just set up parent/child data-binding and the rest would happen automatically. We don't know whether that's applicable though, because you haven;t provided a FULL and CLEAR explanation of the problem, which would include where the items in the controls are coming from. If part of the problem is populating a ListBox, knowing where you're populating it from is part of the problem.