This page links to some of the major online sources for finding United States and multilateral treaties.
For a more places to find the texts of treaties, and for advice on treaty research, see the Treaty Research - Basic Resources guide.
Treaty commentaries are somewhat analogous to annotated codes. They point you to books, articles, or other documents about the treaty, to drafting history, and to resources on interpreting specific language. Consider using a treaty commentary when you need in-depth information on the background and possible meaning of a treaty's language, or when you need some ammunition to argue for your preferred way of reading specific treaty language.
This PDF guide explains treaty commentaries and lists the commentaries available at the Zief Law Library.