Books are the bridge between your textbook and scholarly journal articles. They are usually your best resource for "the basics" -- an introduction, overview, and history of your topic. The quickest way to find books is to search the libraries book databases:
Another way to find books is to "browse" -- go to the library's book shelves and take a look.
At Penn State Harrisburg Library, Mechanical Engineering books are in the "TJ" section, on the 3rd floor. However, you may find additional items in the "TA" (General Engineering), "TC" (Hydraulics), and "TS" (Manufacturing) areas, too.
If you are designing a component for a specific type of system, there may be additional areas of the library to explore. For example, if you are concerned with mechanical aspects of building construction, see the "TH" section. Information about mechanical components for vehicles might be found in the "TL" (motor vehicles) area of the library.
The "T" list within the Library of Congress Outline tells you which topics are shelved under which sections.