How to render Few Custom Fields Based on the value selected in the picklist?

How to render Few Custom Fields Based on the value selected in the picklist? Suppose if I select a value  “X” from the picklist, then i should see fields ‘a’, ‘b’, ‘c’. In the  same way if i select a value  'Y " from the picklist, then i should see fields ‘d’, ‘e’, ‘f’