hello,
your question is a little ambigous. But I think I can help.
Have you ever been to a laundry mat? Think of the washers and dryers as objects and the people as threads. When a washer (object)is in use by a person (a
thread) no one else may use that washer (object). When a thread has a lock on a object no other threads may access the synchronized code of that object. All other threads that wish to access the synchronized code are put in a waiting mode (just like when you have to wait on a dryer to open up). when the thread is finished it releases its lock on the object and then may call the object's notify()/notifyAll() meathod and tell the waiting threads that the object is ready. At that point another thread will obtain the lock on the object. hope this helps.
P.S. to all other readers if I am wrong please correct me.