Searching for jellybeans with the above search engine string would include "-site:*.youtube.com" in the query, which excludes results from all youtube subdomains. If you wanted results only from youtube, you just have to remove the hyphen ("-") from before "site:".
There used to be lots of other stuff you could do with searches, boolean AND, NOT, OR, but they were removed or given less priority as search engines became "smarter". NOT ("-") still somewhat works, but google likes to interpret your query loosly and give every freaking result except what you want, even if you exclude a particular word, making that operator less useful. Still works well for excluding whole domains from results, though.