Institutional Review Boards (IRBs) are institutionally based offices that serve to review the research proposed on their campus to ensure the protection of human subjects. If a project does not involve human subjects, it usually does not require IRB review. There are, however, review boards for animal research (see the Institutional Animal Care and Use Committee at CU Boulder, for example.) See CU Boulder's IRB website.
IRBs came into existence to prevent the repetition of research atrocities that occurred in the past, such as Nazi medical experiments and medical racism and violence carried out by doctors in the United States.
IRBS generally base their requirements for research on the Belmont Report, which is a statement of human research ethics and principles published by the National Commission for the Protection of Human Subjects of Biomedical and Behavioral Research. The three main principles are:
To submit a proposal to IRB, you must first complete CITI training, which is usually offered through your institution.
Part of the Research and Innovation Office, CU Boulder's IRB website has many excellent resources to help you understand what you need to get IRB approval and guide you through the process. They provide an investigator manual that details how you should proceed as well as guidance on what kinds of research do and do not need IRB approval.