Like the European system, the Inter-American system is regional. However, in structure it resembles the United Nations system because it has both an O.A.S. Charter-based body and a treaty-based body. The Charter-based body is the Inter-American Commission on Human Rights. The treaty-based body is the Inter-American Court of Human Rights.
The first key document is the American Declaration of the Rights and Duties of Man. You can find the Declaration at the OAS website (Inter-American Commission of Human Rights) in the page called Basic Documents Pertaining to Human Rights in the Inter-American System. The American Declaration was adopted in May 1948, and so predates the Universal Declaration of Human Rights by several months.
The key international agreement is the American Convention on Human Rights. (Nov. 22, 1969, O.A.S.T.S. No. 36, 1144 U.N.T.S. 123). It should be noted that, while the U.S. signed the Convention in 1977, the U.S. has not ratified the Convention, and so is not a party to it.
The Convention has two important supplementary agreements: the Additional Protocol to the American Convention on Human Rights in the Area of Economic, Social and Cultural Rights ("Protocol of San Salvador") (Nov. 17, 1988, O.A.S.T.S. No. 69, 28 I.L.M. 1641) and the Protocol to the American Convention on Human Rights to Abolish the Death Penalty (Aug. 6, 1990, O.A.S.T.S. No. 73, 29 I.L.M. 1447).
The Inter-American Commission on Human Rights has a wide scope of activity. It is authorized to receive individual complaints charging violations of both the American Declaration and the American Convention. A collection of the commission's decision's, excerpted from the annual report, is now available on the Commission's website.
The Commission also carries out country studies and thematic reports. An example of the former is the 2016 report, Situation of Human Rights in Guatemala.
An example of the latter is the 2016 report, Violence, Children and Organized Crime. In addition, the Commission has created special "rapporteurships". An example is the Rapporteur for the Rights of Indigenous Peoples.
The Inter-American Court of Human Rights is a true judicial body, comparable to its European counterpart, although it does not have the same caseload. The Court publishes its decisions in two main series: Series A- Advisory Opinions and Series C- Decisions and Judgments. The Court also publishes decisions in two series that do not have letters: Provisional Measures and Monitoring of Compliance with Judgments. It should be noted that the Court's decisions are available for a significant time only in a language other than English (Spanish or Portuguese). A comprehensive collection of the Court's decisions is available on the Court's website under the link to Jurisprudence.
The secondary literature in English on the Inter-American human rights system is rather sparse.
The English-language law review literature on the Inter-American system can be found using the standard law review indexes, as well as the Index to Foreign Legal Periodicals.
The following is a brief list of useful sources.
The Practice and Procedure of the Inter-American Court of Human Rights (2nd ed.) by 
The Inter-American Court of Human Rights: Case Law and Commentary by