Primary and foreign key function in php

Question

I have a school project where we need to register student and then let them choose which
sports they want to join. My problem is I don't get why do I need to use Primary key and
foreign key. Can you tell me in as simple word or example.
-17 years old kid

Answer 1

//The primary key consists of one or more columns whose data contained within is used to uniquely identify each row in the table. You can think of the primary key as an address. If the rows in a table were mailboxes, then the primary key would be the listing of street addresses.

//A foreign key is a set of one or more columns in a table that refers to the primary key in another table.  There isn’t any special code, configurations, or table definitions you need to place to officially “designate” a foreign key.

//for details description here is source
https://www.dotnettricks.com/learn/sqlserver/difference-between-primary-key-and-foreign-key

Answer 2

Thank you sir for the meaningful reply now I get what it means after searching for a long time.