The thesaurus is a system of topical terms that can describe extensive connections which system has been developed by the National Széchényi Library for public libraries.
You can search the newest version of the thesaurus
here.
Searching and browsing in the thesaurus is only different from searching/browsing for documents in the feature that the hits will be thesaurus records.
When viewing records, you can detail the connections between records and you can browse among them and find which documents are about a given topic.