That really depends on which index you've chosen. At minimum, any index will allow you to search by article Author or by Subject. Some indexes provide a subject heading list or Thesaurus to help researchers determine which headings are most relevant. Some indexes, especially the online ones, allow you to search other elements, such as words in the periodical title. Each index is different.
Most indexes provide help pages or screens to get new users started.
Reference Librarians will also help you find the best way to use an index. Citations , sometimes with added descriptive elements, like abstracts and key terms, are listed to help you determine which articles are most relevant. The citations also provide enough information to locate the article, and to document it in a bibliography should you use the article in an assignment. The Library subscribes to about 2500 periodicals. That's only a fraction of the number of periodicals published world-wide.