$1.$ What are primary and foreign keys? Explain in detail. What are the implications of using these keys in different tables?

$2.$ What is data dictionary? What is it used for?

$3.$ What is the significance of creating a column in a table? What is the significance of a row in a table?

$4.$ What is referential integrity and how is it used in relational databases for adding, removing and updating rows?