All the minimal super key with no redundant attributes is known as candidate key.

Lets consider, a relation called Emp

In the above relation only two set of attribute can declarred as candidate key out of the six super keys, because other four keys have redundant attributes that are not necessary for unique identification

• {Emp_SSN}
• {Emp_Number}

Therefore, these two sets of attributes are candidate keys among the all other sets.

Note
All the candidate keys are super keys, but not vice versa. Because candidate keys are the sub set of super keys.