Open the METASPLOIT Web GUI in the browser, payloads, exploits and such are all in there, its pretty self explanitory.. Just as an example, you get access to a network, under SAMBA shares all the NetBIOS enabled machines will show up, first thing, run NMAP and take a good look at what services they have running on the entire network, scan the entire IP range, if you see a Windows XP Box running SP2, then you can inject that machine with an exploit which will drop you into the windows 32 command shell. From there you can do what you like, disable something important like their anti-virus and upload a remote back-door for example.
Or you could do the nice thing, look but don't touch, but where's the fun in that!?
I once got onto a network with 245 networked windows machines.. it was exploit heaven!!!
Here's a great site with stuff you can upload remotely into their Start up folder... The flasher one with a picture of Goatse.cx loaded into it never gets old...