Use of DECLARE and SET in MySQL stored program

DELIMITER $$                    -- Change the delimiter

DROP PROCEDURE IF EXISTS demo$$ -- Remove if previously exists
CREATE PROCEDURE demo()         -- Create Stored Procedure
BEGIN                           -- Start of definition
    DECLARE my_int INT;         -- Declare variables
    DECLARE my_big_int BIGINT;
    DECLARE my_text TEXT;

    DECLARE my_name VARCHAR(30) -- Declare variables with 
        DEFAULT 'Rookie Dev';   -- default value set

    SET my_int = 20;            -- Set variables to values
    SET my_big_int = POWER(my_int, 50);

END$$                           -- End of definition
DELIMITER ;                     -- Reset the delimiter