The Performance tool shows you information about how your computer is currently performing.
CPU Usage offers a gauge and chart which show you how busy your computer's CPU is at the moment. In the case of multicore or multi-CPU computers, an average for all the cores is calculated and displayed.
Internet and network connections shows you the current download and upload speed, and also the IP addresses, Mac addresses, and the connection's speed.
A Mac address is the physical address of the network interface you use. This is sometimes needed for network configuration and also when discussing with your ISP (internet service provider).
The connection speed is expressed in Mbps (millions of bits per second) and represents the maximum speed of the network interface. This speed is usually quite high, but if this is an Internet connection, that speed is never reached because of limitations that your ISP impose.
The Memory taken by the running programs chart shows you which programs take the most memory on your computer, as reported by Windows. The Refresh button refreshes this chart.