Little suggestion: use UI instead of SQL
But...
CREATE PROCEDURE GetInfo(@CourseName VARCHAR(30))
AS
BEGIN
DECLARE @tmp TABLE (CourseName VARCHAR(30), CountOfStudents INT)
INSERT INTO @tmp (CourseName, CountOfStudents)
SELECT C.CourseName, COUNT(S.StudentId) AS CountOfStudents
FROM CourseTable AS C INNER JOIN StudentTable AS S ON C.StuID = S.StuID
WHERE C.CourseName = @CourseName
DECLARE @stu INT
SELECT @stu = CountOfStudents
FROM @tmp
SELECT 'Dear Faculty, ' + @CourseName + ' candidates is: ' + CONVERT(VARCHAR(10), @stu) + '.' AS Info
END