how to declare procedure in sql code example

Example 1: create procedure sql

CREATE PROCEDURE SelectAllCustomers @City nvarchar(30), @PostalCode nvarchar(10)
AS
SELECT * FROM Customers WHERE City = @City AND PostalCode = @PostalCode
GO;

Example 2: declare variable in stored procedure in sql server

DECLARE 
    @product_name VARCHAR(MAX),
    @list_price DECIMAL(10,2);

Example 3: procedure in sql

-Stored procedure is a group of SQL
statements that has been created 
and stored in the database.
-A stored procedure will accept input 
parameters so that a single procedure
can be used over the network by several
clients using different input data.
-A stored procedures will reduce
network traffic and increase the performance. 
If we modify a stored procedure all the
clients will get the updated stored procedure.

Sample of creating a stored procedure
CREATE PROCEDURE test_display AS
SELECT FirstName, LastName FROM tb_test
EXEC test_display