In the emacs tutorial, you will have seen how to split an emacs screen into as many components as desired. However, sometimes it's more convenient to have another emacs window open, instead of having a split screen. What you don't want to do is start up another emacs session (and therefore be running another process on your machine).
Rather, you can splinter off another emacs window while still only running one emacs process. You can do this by typing Ctrl-x 52 in your original emacs window. This will spawn a new emacs window, within which you can read in another file, etc. To close this new window, type Ctrl-x 50 in your chosen window. It will then disappear and revert back to one emacs window.
You should have a go at doing this a few times to get the hang of it.