You can make certain fields in the system mandatory, optional, read only or disabled in two different ways.
Field Settings
Go to Setup and click Settings.
Click Field Settings.
Search for key words relating to the field setting (i.e Continuous if you are searching for the Continuous Service Date field).
Click the field setting.
Change the value in the Display dropdown to one of the below:
Disabled
Mandatory
Optional
Read Only
Tick the Include box to display this field or leave it unticked in order to hide it.
Click Save.
Edit Function
Open up the area where the field is situated on the system.
Click the small Edit button in the bottom left hand corner of the system.
This will now highlight any editable fields.
Click the highlighted field you wish to amend.
Change the value in the Display dropdown to one of the below:
Disabled
Mandatory
Optional
Read Only
Tick the Include box to display this field or leave it unticked in order to hide it.
Click Save.
Once you've completed the steps above, run a Batch Update to bring all changes up to date.