To the best of my knowledge, these are trustworthy, informative posts, correctly outlining Google's advanced search syntax as of now:
I recommend looking through these posts to learn about all the operators Google offers.
And here is a warning: many other online tip sheets and example searches have outdated or wrong info.
Here's an article, worth reading, from Karen Blakeman: GUARDIAN’S TOP SEARCH TIPS FOR GOOGLE NOT QUITE TIPTOP, It discusses this post from the Guardian.com and its not quite tip-top content.
I can name others who have posted tips that, unfortunately, don't match the reality. Here is an example - How to find candidates by keyword (skills and experience) - from Workable - which has multiple mistakes. For example, it lists AND as an operator (it's not); states that the Asterisk * makes Google search for variations of a word (it doesn't); says that parentheses () group words, while they don't make any difference in Google. Other tip sheets from Workable have mistakes as well. I could name a dozen more other sites with incorrect information (ask me if you are curious).
Some typical mistakes in the questionable posts include the plus +, which is no longer an operator; using AND and the parentheses; using the asterisk as part of a word; listing the operator NEAR (it doesn't work on Google); listing the operator link: that no longer works; and suggesting to search for email addresses by using the symbol @.
Conclusion: don't blindly trust various "Google Boolean" posts - read them with a grain of salt. Compare what those posts say with the correct sources that I listed at the beginning of this post, to see what's right and what is a mistake. It wouldn't hurt to try example searches if you are unclear how particular search syntax works.