This really is a mac thing...its a great feature, but just odd at first for a switcher...its will take a bit of time, but you'll appreciate that now you can drag images/text to the desktop/an application, and be able to have multiple windows...
I guess you're using Safari, and for a new user, I recommend these:
There's no function key for this, but you don't really need one. There are things called Bookmarklets that are very useful for this sort of thing, at least in web browsers. Do a Google search for bookmarklets and you'll see what I mean