Controlling field is driving dependent field. Standard and custom checkboxes and picklist can be controlling fields. The field that has its values filtered is called the dependent field.
Setup > Customize > Select Object (Accounts) > Fields > Field Dependencies
Field Dependencies > New
Controlling Field: Account Source (Picklist Field)
Dependent Field: Active (Picklist Field)
Now we have first row as Account Source (Controlling Field) with all the picklist values in the columns. Then we have Active (Depending Field) with all its picklist values.
When I select Account Source as Web then the depending field (Active) can be “Yes”. Similarly when I select Account Source as Partner Referral then Active field can be “No”. When I select Account Source as Other the Active field can be "No or Yes". This can be done by using Include Value and Excludes Values buttons.
Field dependencies is created.