A indulgence is a from of penance. As an example, if, on the feast day of St. Francis, if you go to confession (within a week), receive Holy communion (also within a week), lose all attachment to sin, and make a pilgrimage to Steubenville, OH and spend time in prayer (i believe it is an hour for the intentions of Pope Benedict) at the Portinicula Chapel at Franciscan University of Steubenville, you can receive a plenary indulgence. …"
I did research into this topic about a year ago and found that “it is sufficient that these sacred rites and prayers be carried out within several days (about 20) before or after the indulgenced act.” See item 5 at this Vatican link:
vatican.va/roman_curia/tribunals/apost_penit/documents/rc_trib_appen_pro_20000129_indulgence_en.html
In addition to being Catholic, not excommunicated, and having the general intention of receiving the indulgence, the conditions for an indulgence given in the above link are:
"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.
"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."
The complete detachment from sin, even venial sin, is called perfect contrition. It that is not present, it becomes a partial indulgence.
All Catholics, Eastern and Latin, that are not excommunicated and in a state of grace by the end of the performance of the indulgence, can receive an indulgence, or assign it to the faithfully departed.
All prior general indulgences revoked in 1968.
Published in:
Enchiridion indulgentiarum: normae et concessiones
Editions:
1 June 28, 1968
2 October 1968
3 May 18, 1986
4 July 16, 1999
Approved US English translation: Manual of Indulgences, USCCB, 2006.
The appendix of Manual of Indulgences contains the doctrine, which is also here:
vatican.va/holy_father/paul_vi/apost_constitutions/documents/hf_p-vi_apc_19670101_indulgentiarum-doctrina_en.html
It you get the book, most of the footnote quotes are included, and all the approved indulgences are described.
For DS footnotes use Denzinger:
catecheticsonline.com/SourcesofDogma.php