go to start>run>cmd>when the prompt appears, type in
ping website or IP
ex: ping
www.yahoo.com
then you will get
pinging www.yahoo.akadns.net [their IP] with 32 bytes of data:
followed by four replies (you can change this setting with different commands such as continuous replies until you stop them. Just google those if you want to get into the advanced ways of pinging.
Then after that you'll get a ping summary. Loss of 100% is obviously a problem.
If you know the IP address instead of the website address for example another computer on a network, you use that instead of a URL.