Primary Keys: Primary keys are the identifier and applied 
on the table in the form of constraints. Primary key 
provides uniqueness in the data.

Foreign Key: Foreign Keys are the relationship and applied 
on the table in the form of constraints. Foreign key in a 
table is a primary key of another table and use to make 
relationship between two tables.

example :

primary key table: emp ( ENO, ename, address)
here eno is primary key

foreign key: table hari( ENO, phone, salary)
here same eno from hari table is used to get the values 
from emp.