machan that cout function is in iostream namespace. so you have to import that before compilation. thats why you got an error saying cout - undeclared identifier.
and getch is using to hold up the screen while key is pressed. otherwise Hello world will print. but the screen will pop and vanish in seconds. getch function is in conio namespace. so you better import it.
after importing the namespaces, you ve to use the keywords "using namespace" to bring the actual functionality out. then the program allows you to use any function in the std namespace. (in this case which is cout.)
you press F6 or build solution after this. and then press start debugging or press F5.
hope this helps.