Traditionally, the library catalog has been a searchable listing of items owned by the library: print and electronic books, journals, government documents, videos/DVDs/CDs, etc. Increasingly though, libary catalogs also contain records for selective websites and documents freely available on the Internet.
You generally use the library catalog:
NOTE: You typically cannot use the library catalog to find individual articles within a journal--you may need to use a separate journal index/database for that (see Finding Articles)--although many libraries are now purchasing "discovery" tools that allow the searching of the catalog and article databases together in one search.
To search the library catalog by topic, begin with a keyword search: type in one or more search terms representing the main concepts of your search (e.g., "pesticide residues and food"); click on a title of interest and use the subject links in the catalog record to locate other books on the same topic. You can use the truncation symbol (usually an *) to retrieve alternate forms of a word (e.g., food contamina* will find food contamination, food contaminants; food label* will find food label, food labels, food labelling).
It is likely that your university library will not have everything that you need for your research; however, most will arrange to get what you need, for free, by borrowing books or requesting photocopies of articles from other libraries. This service is called Interlibrary Loan and is only offered to currently affiliated faculty, staff, and students. You may need to set up a free account before submitting requests. Information is available for MSU users; you may need to contact your university library for specific directions.