Don't fret too much. By default this is Google-like (ANDing all of your terms). You can easily narrow your results using the facets on the left. You can easily re-sort your results.
Here is OCLC's handout on searching. We could make something similar showing U.K. examples.
Most WorldCat records are indexed using Library of Congress subject headings. Browse the LC thesaurus to find the authority terms.
Your searching universe
By default you are searching WorldCat.org. You can add many more, delete WorldCat.org, etc.
Use the Advanced Search to make your selections.
The Advanced search form will list all the fields available to you. You get more fields, more precision, when you search fewer databases. Here are some of the fields available for searching in the WorldCat database. (The WorldCat.org database has fewer searching fields.)
Phrase searching is also available, e.g, se=advances in libr*
uky.worldcat.org
Working Group members:
"The group is charged to review WorldCat Local’s current configuration for possible enhancements based on OCLC’s continuing product development; to recommend a process for changing settings, adding new resources and for communicating those changes going forward; to research the possibility of participating in the WorldCat knowledge base for improved resource sharing of electronic journals; and to conduct informational sessions focused on the capabilities of the WorldCat Local discovery system."