Static data field - the field is set at the start of the program (if creating a program) and can not be changed, its value will be constant.
Instance data field - can be manipulated by the user, so that its value can be stored: for example you have a data field storing how many hours a person can work in one day, the field will be static as there are always 24h in a day and that can not change.
If you have a second data field storing how many hours a certain employee worked that field will be an instance data field as its values can differ.
