Once you have a citation for document, it's easy to find the document.
Citations might come from the bibliography of another article/book, a list of suggested readings from a textbook, a Prof, an online source, etc. They provide the information required to locate the document.
It's essential that you understand how to read a citation, to establish whether it's a book or a journal, and to identify the title of the larger work in which it was published.
Then look up the title in Omni.