question about branching

[Largent, Jim]

I am very familiar with RCS and have just started using CVS and I have a
question about branching.  In RCS I could check out a previous version of a
file, change it and check it back in.  RCS would create a branch off the
version that I checked out.  When I tried to do this with CVS, it wouldn't
let me saying that a branch needed to be created.  From looking at the
documentation, I have the following question.  Does everything have to have
a label and then a branch created using that label?  Does this branch every
file in the repository?  
Thanks