A repository is a free online collection of documents, often scholarly. There are several kinds:
When a journal article is included in a repository, it will often not be identical to the published version. It may be an earlier version, before final corrections were made for publication. The same may apply to some other kinds of material. So if citing an item from a depository in an assignment, please ensure you make clear which version you have consulted. The SIA librarians can help if necessary.
Much material in repositories is available in full, but sometimes you will only have access to a citation (a brief description) instead of the whole text.