[Newbie] Committing .. and then?

Hi,
Sorry for the newbie question;  I'm reading through some online tutorials
to try to work this out, but I can't find anything to explain what must be
a really simple problem.

I have a directory of files imported into CVS.  I then delete the
originals, and 'checkout' the same files back into the working directory,
where I proceed to edit them.  So far, so good?

When I've changed the file, I save it and 'commit'.  OK, it tells me that
the changes have been recorded, and if I do cvs log <filename>, the
comments I added are all there.  Good.

But, here's what I can't answer: if I want to edit that file again, do I
have to check it back _out_, before editing it?  When I do 'cvs checkout
<filename>', I get a message that the module can't be found.  Two
questions:

1.  does this mean that I no longer need to checkout the same file?  Even
if I walk away from my computer and don't touch the file for another week?
Is it still 'checked in'?  If so, how do I get it back out when I _am_
ready to edit it again?

2.  how do I tell the system 'OK, all done', and that my editing session is
over, and that I'm off to watch a film, smoke a reefer or go out for a jog?  

Thanks in advance.