You can search based on combinations of any of the searchable fields. Start with the topmost line and pick a field on which to search. When you have selected it, the form will allow you to either enter a search string for that field, or pick from a list of options (depending on the field you have selected).
If there is a list of options, you can select multiple entries by using Ctrl-Click (or Apple-Click on a Mac). Multiple words in typed entries will be used as multiple search keys.