well, apache is not an operating system but a server software. So you will need an existing operate system already installed before you attempt to install apache.
The SME Server package is not such an addon but a full operating system (including various server daemons). That's what is meant by "Note: this is NOT a product you install on an existing Linux system; this is a complete integrated operating system that you install on dedicated hardware."
What do you mean by setting the server offline?