I love being asked to summarize the Ainulindalë!
In the beginning, Eru Iluvatar sang the concept of the world into being. He was joined in this by the Ainur, his spirit servants. A number of the higher Ainur, the Valar, sang significant parts in the composition. One Vala, Melkor, grew jealous of sharing the beautiful thought of the world, and coveted it for himself, marring the Music as he did so. Eru sang a countertheme to repair the wounding of the world, shutting Melkor out of the Music.
There were three themes to the Music, and the Ainur helped with two of them, but Eru sang the last alone, and the Ainur were ignorant of the shape of that theme.
Then Eru spoke the words of Creation and the Music was made physical, and Arda, the world, was made. The Valar who played major parts in the Music entered Arda as guardians, followed by lesser spirits called Maiar. Melkor, as well, stole into Arda so that he could make his covetous thoughts real as well.
There were 14 Valar, 7 male and 7 female. The greatest were Manwë, and his mate Varda. The others were Ulmo, lord of the oceans, who has no mate; Nienna, Lady of Tears, who also dwells alone; Aulë the Smith and his mate Yavanna, protectress of Nature; Oromë of the Hunt and his mate Vána the Ever-Young; Mandos, Lord of the Dead, and his mate Vairë the Weaver; Lórien, Lord of Dreams, and his mate Estë, the Gentle; and the Warrior, Tulkas and his mate Nessa. Melkor, later known as Morgoth (“Black Enemy”), was once counted among the Valar, but was cut off from their company before the World was made.