When you first open Performance Monitor (perfmon), you see the following:
Let's briefly go through each one and talk about what they do.
At the very top level "Performance" gives you an overview of your systems memory usage, network usage, disk usage, etc. You can right click on "Performance" and connect to another computer to view a remote computers performance statistics. (NOTE: Should add brief comments about what is required in order to remotely connect to another machine…)
From the Monitoring Tools icon you can right click and launch the Resource Monitor. Resource Monitor is another powerful tool that can help you see how your system resources are being used. You also have the ability to launch the System Reliability Monitor. This utility allows you to see information about software updates and installations. You can also see critical events that occurred and on what day those events occurred. Finally, you can see all of the problem reports that have been sent from your computer by clicking on the "View all problem reports" link at the bottom of the window.
The Performance Monitor is primarily for viewing real time statistics. By default only one counter is selected; the %Processor Time counter. However you can add additional counters by clicking on the green plus sign. This will allow you to monitor any counters you wish in real time.
While you can see all of the performance counters you like here, the real power of Performance Monitor is found in its ability to capture performance metrics over an elapsed period of time. Capturing data over a period of time allows you to see trends and these trends are what are most useful for determining the overall performance of your system. To capture this data, you can create what are called "Data Collector Sets".