I have a question here. I have a search.php file that does the functions, jquery to retrieve search values entered by users. However, is it also possible that I have a jquery .get javascript that calls search.php file's particular php functions instead of calling other php files to do more data retrieving from database when a certain event is executed (e.g. clicked on the result)?
Yes.
You can get or post to whatever you want, provided you don't run into any cross-domain issues.
You can only perform HTTP requests on URLs. Since, in PHP, URLs translate to whole files and not functions, you can only perform a request on a whole file. You will need to call the function yourself within that file.
Your question is a bit confusing...
No, you can't call directly a php function with javascript. You can, however, pass a parameter to the page that contains the function. So, you can call different functions based on what parameter was passed
Yes, you can call different pages with jQuery.get, just change the url parameter based on your logic