How does thread synchronization work inside the monitor? What level of synchronization should the program do?

In a Java virtual machine, each object (object and Class) is associated with a logical association monitor, each monitor and an object reference, in order to implement the exclusive functionality of the monitor, each object is linked with a lock.

Once a method or block of code is synchronized modified, this part is placed in the monitor's monitoring area, ensuring that only one thread executes that part of the code at a time, and that the thread must not allow execution of that part of the code until the lock is acquired.

Java provides two locking schemes for display monitor (lock) and implicit monitor (synchronized).

How does thread synchronization work inside the monitor? What level of synchronization should the program do?