A working copy is the copy you have checked out to your working area. It doesn’t matter if it is a branch or from the trunk. It’s what you are working on.
You can switch between branches (or more correctly copies) of the same parent with svn switch. This will basically say, what’s different between the current working copy and the branch I am switch to. It then performs an update on your current working copy to the revision of branch you switch to.
So working copy is your checkout, however it was obtained.
Switching is just changing the branch your working copy commits to. Think of it like changing the pointer in the repository where your commits will go. With the aid of acquiring any differences from the branch to your work area.