Is it possible to use quotation marks to set the exact match in the search engine? If yes, how does it work?

For example, I use “Hello Word”
Does it mean I will get all lessons that contain HelloWord expression only? That is to say I will not get the lessons that contain only ‘Hello’ word for example? Or the lessons that contain both ‘Hello’ and ‘Word’ but in different places of the text

The other question is which lessons’ fields are used to find the entrances of search expression? Title, Description, Lesson’s text. All of them or not? Maybe some others …

Quotation marks do not have that effect in the search I’m afraid. The search looks for all words you use in the title, description and text for lessons. We do hope to improve the search feature in future and it would be nice to incorporate that at that time.