Complex sentence: Once the request has been made, control is given to the object immediately; it may choose to do other things, or return control back to the operating system, which typically will schedule other tasks or put the machine to sleep.
Split into simpler sentences: Once the request has been made, control returns to the object immediately. It may choose to do other things, or return control back to the operating system, which typically will schedule other tasks or put the machine to sleep.