What is a wire less network device?

I'm on my computer at my friends house, now my computer isn't programing correctly when i try to at least connect to a network.For some reason they don't work i have been trying to work this computer since last night can some one help first of all i have a toshiba,second of all i have a lot of windows open such as windows network diagnostics,third of all when i put in youtube or meez(my meez username is christinemysis) IT DOESN'T WORK!!!and every time i try connect to my friends modem it doesn't work MY computer keeps saying in quote "plug in a ethernet" or "reinset or whatever it is a rein daptter" PLEASE HELP ME!!!!