Without scheduling, the processor would give attention to jobs based on when they arrived in the queue, which is usually not optimal.
As part of the scheduling, the processor gives a priority level to different processes running on the machine.
When two processes are requesting service at the same time, the processor performs the jobs for the one with the higher priority.
In a multiprocessing environment with more than one logical processor (i.e. multiple cores or hyperthreading), more than one task can be running at the same time.
The Windows Task Manager utility offers a user interface for this at the process level.