where we use article the?

to tell about specific nouns.. he is the principal. there is only one principal in every school, he is the special one to school. and he is "the man/boy" who came yesterday, this is the pen/ book that you gave me. * we should use "the" which is single in universe. ex: the moon, the earth, the taj mahal, the charminar. we can use before books such as the khuraan, the bhagavadgeetha, the Bible. to tell about group. "The tiger" (all tigers are cruel here, at the same time "The rose" all roses are beautiful).