Now that you've been through the in-built emacs tutorial, you should have a basic idea of how to use a few simple commands to edit and save a file.
The following is just to make sure you understand how to invoke emacs in general.
|Suppose you have an existing file called input in your current working directory. You wish to edit this file. Therefore, intead of just typing emacs & at the prompt, intead, you can type emacs input &|
|Now, suppose you wish to create a new file, called data . Even though the file doesn't yet exist, you can type emacs data & to create an emacs session of this new file. After making your modifications, saving, and exiting from emacs, you should find that you have a new file in your current working directory called data|
|Paths to file names also apply when invoking emacs. Say you current working directory is /home/mildred/optim/ and you wish to edit the file data in /home/mildred/ . You could type emacs ../data & to edit this file.|