Here is an example summary of this reading selection:
In his article “In Defense of Multitasking,” Peter Silverman argues that multitasking is a necessity at work because working on one thing at a time causes logjams in workflow for others. Multitasking allows others to get crucial information when they need it, and it gives the multitasker a break from difficult tasks when he or she needs one. Multitasking is especially important for those with a large number of subordinates.
Your summary will differ from this one in the way it is written, but it should include roughly the same information.