Summa Cite allows you to follow up citations to St. Thomas Aquinas' Summa Theologiae (Summa Theologica). If you are reading a work that refers to it, you can put in the appropriate information and go directly to the correct page on the New Advent website.
These citations contain several components. They begin with the identification of the Summa, often abbreviated, e.g., ST or Sum.. Next they indicate the division of the work: it has a three main parts, but the second part is divided into two parts; since St. Thomas had not finished writing it when he died, there is also a supplement that supplies articles that he intended to write; the supplement has two appendices. Abbreviations are used for this second component, also: parts one and three are generally given simply as Ia and IIIa; section one of part two is IaIIae; section two of part two is IIaIIae. The third component of these citations indicates the question number and the fourth the article number. The citations often continue to provide a more precise location, but the mechanism provided here does not go beyond the article level.
You can go to the beginning of a question by putting "0" in the Article field. Try this if you get a "file not found" response. You can go to the beginning of one of the major divisions by putting "0" in the Question field. You can go to the beginning of the Summa by way of the link at the top of the page (associated with the words Summa Cite).