The Catholic Church derives its authority from Sacred Scripture, Tradition and the Magisterium and the latter publishes document in order to teach the faithful and the world at large.
Church documents come in different forms with various levels of authority. Here is a list of some of them you may come across. Most of these are available online.
Papal Encyclical: (Encyclical is the Latin word for a circular letter) A “letter” sent from the Pope in his capacity as the head of the Church to whole the Church, concerning an area of doctrine. Papal encyclicals have the highest priority.
E.g. Benedict XVI, Deus Caritas est – encyclical: God is Love.
Apostolic Constitution: a document which includes solemn magisterial acts of the Church regarding governance of the Church, dioceses, papal elections etc.
E.g. Benedict XVI, Anglicanorum Coetibus – providing for personal Ordinariates for Anglicans entering into full communion with the Catholic Church, and John Paul II, Fidei Depositum – at the front of each copy of the Catechism of the Catholic Church.
Apostolic letter: From the Pope on a particular theme or to a particular group of the faithful, e.g. to the youth, or the people of a country, or to the bishops etc. They have a little less authority than encyclicals.
E.g. John Paul II, Apostolic Letter Rosarium Virginis Mariae – on the Rosary
Motu proprio: (Latin for on his own impulse) is a document issued to either the whole Church or a part of it, by the Pope on his own initiative, and personally signed by him.
E.g. Benedict XVI, Apostolic Letter issued “Motu Proprio” Porta Fidei for the Indiction of the Year of Faith
Apostolic Exhortation: a document produced by the Pope in His capacity as the successor of Peter which encourages (exhorts) the faithful in their attitude to the life of faith. Often these come out of synods of the bishops.
E.g. Benedict XVI, Verbum Domini
Dogmatic constitution: These are key documents which define Church teaching.
E.g. Vatican II, Dogmatic constitution on the Church, Lumen Gentium.
Teachings of the congregations: where departments of the Roman Curia (led by cardinals in Rome) clarify teaching or produce teaching documents,
E.g. Congregation for The Clergy, The General Directory for Catechesis.
Papal Audience: The regular teaching of the Pope (e.g. the Wednesday audience at St. Peter’s in Rome), or private audiences when he also gives teaching.
Homily: teaching given during Holy Mass on the Scripture readings of the day.
Discourse: Teaching outside Mass, may be when the Pope is travelling or visiting people.