How do we check for live hosts?
First we are going to be scanning to check what ports are open and OS (Operating System) fingerprinting. But before we do that your probably wondering how do we check if people are on the network and if they are what are their IP addresses. Well What I do and believe it is the easiest way by far is running ettercap. So lets run ettercap open up a console and type in.ettercap -G and ettercap will open up.
How do we scan for ports and know what OS he's using?
Okay pick an IP address from the list and remember it. Now open up a new console to scan the victim with namp. Now nmap has a lot of options so it's really easy to get confused.but I don't want to talk too much about it just yet. So now back to our console type in nmap -O [your victims IP] . The -O options is Operating system detection. Then you should get something like this. Now just by looking at this we know its a Windows XP with our favorite port open 445 SMB.
The complete tutorial here