pinging is the process of sending a data packet from you one machine A to another machine B, and back. The ping will be the amount of time(usually measured in milliseconds) that an acknowledgement(ACK) from machine B to reach A again. It is a measure of latency and not bandwidth, which is important for frequent random data accesses(such as online gaming), but relatively unimportant for operations such as large file downloads(which depend more on throughput/bandwidth).
To ping your ISP, the easiest way to do it, assuming you have access to a DOS shell, is to type the following:
ping <your_isp>
This command will send 4 packets to <your_isp> and measure its delay/ping, giving an average ping after all 4 packets are completed.
<your_isp> can be either numerical or canonical, i.e. it can be its IP address(eg. 192.168.0.1) or its name(eg. home.com)
To obtain more accurate results, try pinging with more packets, such as 10. You may use a -n argument to specify the number of packets to send, eg. ping -n 10 home.com to ping home.com 10 times.