Applications can use event objects in a number of situations to notify a waiting thread of the occurrence of an event. For example, overlapped I/O operations on files, named pipes, and communications devices use an event object to signal their completion.
The following example(From MSDN)uses event objects to prevent several threads from reading from a shared memory buffer while a master thread is writing to that buffer. First, the master thread uses the CreateEvent function to create a manual-reset event object whose initial state is nonsignaled. Then it creates several reader threads. The master thread performs a write operation and then sets the event object to the signaled state when it has finished writing.
Before starting a read operation, each reader thread uses WaitForSingleObject to wait for the manual-reset event object to be signaled. When WaitForSingleObject returns, this indicates that the main thread is ready for it to begin its read operation.