Please explain different types of keys in a relational database

What are the different types of keys in RDBMS,
I know, A key refers to an attribute/a set of attributes that help us identify a row (or tuple) uniquely in a table (or relation). A key is also used when we want to establish relationships between the different columns and tables of a relational database. The individual values present in a key are commonly referred to as key values.
But i'd like to know what are different keys and at what situations are they useful