Show hidden field according to selected item from dropdown

I’m new to GC and i can’t find the way to do the following:

  • In Add or Edit forms, i need to show/hide a checkbox field according to the selected value in a dropdown list.
  • In fact, according to the selected value of the dropdown list, i need to get a value from another field of the same table and, according to that field value, show or hide the hidden field.

Thank you for your help.