The video gives instruction in Latin by means of the Mass, attended by virtually every saint since AD200-300. The pronunciation is ecclesiastical Latin, which the Church developed.
Some vocabulary: declension - nouns; conjugation - verbs; vocative (root for vocal or voice) - nouns, pronouns, and adjectives used to address or invoke a person or thing.
The priest and altar boys quietly pray Psalm 42 at the beginning of Mass, but it is preceded by the following:
In nomine Patris, et Filii, et Spiritus Sancti. Amen.
P. Introibo ad altare Dei.
R. Ad Deum qui laetificat juventutem meam.
In the name of the Father, and of the Son, and of the Holy Ghost.
P. [Priest] I will go to the altar of God.
R. [Response from altar boy] To God, Who giveth joy to my youth.
Roman Missal 1962