You can start by searching in Scholar for materials and, if you find secondary sources, you can use them to find primary sources. For example, many secondary sources cite primary source documents in among their references or in their footnotes. You may also find a guide to research in your subject area that lists useful primary sources and where they can be found.
Some useful keywords to try:
If your research is Cleveland-related, you may also try our Special Collections and/or the Cleveland Memory online collection (see below).