Dear Dan:

Background on Indulgences can be learned from the Catholic Encyclopedia article on Indulgences. EWTN has a short article on the General Conditions required to gain an indulgence.

The actual document on Indulgences is on the Internet: Norms and the List of works qualified for an Indulgence.

The general info from the Vatican's offices of the Apostolic Penitentiary document, The Gift of Indulgences is:

General Remarks On Indulgences

1. This is how an indulgence is defined in the Code of Canon Law (can. 992) and in the Catechism of the Catholic Church (n. 1471): "An indulgence is a remission before God of the temporal punishment due to sins whose guilt has already been forgiven, which the faithful Christian who is duly disposed gains under certain prescribed conditions through the action of the Church which, as the minister of redemption, dispenses and applies with authority the treasury of the satisfactions of Christ and the saints".

2. In general, the gaining of indulgences requires certain prescribed conditions (below, nn. 3, 4)...

3. To gain indulgences, whether plenary or partial, it is necessary that the faithful be in the state of grace at least at the time the indulgenced work is completed.

4. A plenary indulgence can be gained only once a day.In order to obtain it, the faithful must, in addition to being in the state of grace:

— have the interior disposition of complete detachment from sin, even  venial sin;
— have sacramentally confessed their sins;
— receive the Holy Eucharist (it is certainly better to receive it  while participating in Holy Mass, but for the indulgence only Holy Communion  is required);
— pray for the intentions of the Supreme Pontiff.

5. It is appropriate, but not necessary, that the sacramental Confession and especially Holy Communion and the prayer for the Pope's intentions take place on the same day that the indulgenced work is performed; but it is sufficient that these sacred rites and prayers be carried out within several days (about 20) before or after the indulgenced act. Prayer for the Pope's intentions is left to the choice of the faithful, but an "Our Father" and a "Hail Mary" are suggested. One sacramental Confession suffices for several plenary indulgences, but a separate Holy Communion and a separate prayer for the Holy Father's intentions are required for each plenary indulgence.

6. For the sake of those legitimately impeded, confessors can commute both the work prescribed and the conditions required (except, obviously, detachment from even venial sin).

7. Indulgences can always be applied either to oneself or to the souls of the deceased, but they cannot be applied to other persons living on earth.

Intention to Receive an Indulgence: One must at least implicitly intend to receive the indulgence. The language of the Norms is, "one must have at least a general intention to gain them".

When you seek an indulgence your intention can be to apply it to yourself or to someone specific, or to all, in purgatory. There is no formal prayer for this. It is your interior intention that determines this.

An "habitual intention" is when a person consciously and deliberately intends to seek an indulgence (for self, someone or all in purgatory) anytime they happen to perform a qualifying work. In otherwords, the person intends a overall and general intention without having to specifically say the intention each and every time they perform a qualifying work.

God Bless,
Bro Ignatius Mary