Essentially, how the heck do I get Filemaker to know that my drop down box is a find selector, and not a data input?
FileMaker "Knows" by the window mode that you are in. If you are in Browse mode, selecting from the drop down will enter data. If you are in Find mode, selecting from the same drop down specifies find criteria on that field.
Thus, the simplest way to do what you want is to click the Find button in the Tool bar, select from one or more of your drop downs and then click the same button again.
More sophisticated options use a script to search your database. In those cases, you often do not use the same drop down, but add a new field with global storage for each drop down where you can specify your search criteria in browse mode, then you click a button and the script uses the data in the global fields to perform the find for you. You can find examples of this method here: Scripted Find Examples
Concise and exactly the information I needed. Thank you for the link.