Volatile keyword in Java - Clarification

I am really confused about what I read about the applications of volatile keyword in java.

1. Is the following statement correct? "a write to a volatile field happens before every subsequent read of the same field"

2. Ideally when should volatile keyword used?

3. What is the difference between:

   class TestClass
   {  private int x;
   
      synchronized int get(){return x;}
      synchronized void set(int x){this.x = x;}
   
   }
   

and

class TestClass
{  private volatile int x;

   int get(){return x;}
   void set(int x){this.x = x;}

}