One-to-One relationship can be implemented as a single 
table and rarely as two tables with primary and foreign key 
relationships.
One-to-Many relationships are implemented by splitting the 
data into two tables with primary key and foreign key 
relationships.
Many-to-Many relationships are implemented using a junction 
table with the keys from both the tables forming the 
composite primary key of the junction table.

It will be a good idea to read up a database designing 
fundamentals text book.

Excellent!!! Swapna. Really good...

All relationships are implemented by primary key and 
foreign keys.
One-to-one
When we use two tables to relate by one primary key in one 
table and one foreign key in secound table.
for example Employee table and salary table.
One-to-many
When we use many table but primary key is only in one table 
and in other tables we use foreign key to inter-relate 
tables.
For example Emp_id(primary key) in Employee table is 
assosiated with salary_emp_id (foreign key) in Salary table 
and associated with tax_emp_id (foreign key) in 
tax_collecation table and associated with pf_emp_id 
(foreign key) in provident_fund table.
Many-to-many
When we use primary keys of two or more tables in a 
saperate table and in this table we relate these with other 
tables by foreign key and primary key