EXAMPLE: find criticism on "As I Lay Dying" by William Faulkner -
1. Go to the "Library Catalog" tab and click the "Author/Subject Browse" link. 
2. Type "Faulkner, William" into the search box and click the "subject" button to browse works about Faulkner.
3. Browse displayed subject headings for most relevant results. (The number to the far right of each subject heading indicates how many works the library possesses that correspond to that subject heading.)
4. Look for a sub-heading matching the title of the work. The books listed under this sub-heading will often have criticism over the work. (For example, Faulkner, William, 1897-1962. As I Lay Dying).
5. Look for the subheading "criticism and interpretation." If one doesn't exist for your particular work, examine the general critcism items on the author.
6. Get the book from the shelves and scan the table of contents and index to determine if it will be useful to your research.
Your instructor may tell you to use an essay in a collection (also called a selection from an anthology) as a source. This is an essay by one critic collected in a book with other essays by other critics.
Collections and anthologies are listed in the library’s catalog like other books. The key to identifying them is the Details button. Click the Details button, then click the Catalog Record tab, then find the Title field.
After the title, a name is listed. If this person is listed as an editor, the book is a collection.
A scholar named Harold Bloom has edited many collections of criticism. Do a keyword search in the library’s catalog for your author’s last name plus the words and Bloom (for example, "faulkner and bloom"). You’ll probably find a collection on your author edited by Harold Bloom.
You can also find essays in the MLA International Bibliography (see Finding Articles). Essays are listed as book articles.