Find the names and descriptions of courses that belong to the subject named "Computer Science".
SELECT T1.course_name ,  T1.course_description FROM Courses AS T1 JOIN Subjects AS T2 ON T1.subject_id  =  T2.subject_id WHERE T2.subject_name  =  "Computer Science"
courses that belong to the subject named 'Computer Science' refers to a JOIN operation between Courses and Subjects tables on subject_id with a WHERE condition on subject_name = 'Computer Science'; names and descriptions of courses refers to course_name and course_description from Courses table;