Perhaps the most known and used operator is the site: operator, which limits a search to a single site. For example, if I wanted to find all Disney related pages on Twitter, I might search for (remember, no spaces between site: and the site you’re searching):
disney site:twitter.com
As you can see, all the results are on twitter.com.
This operator is really useful on large sites that have poor search functionality – for example, searching Javadocs or social media sites such as Reddit.