You seem to possible be aware that you are using the same shell on both Ubuntu and Mac OS X (that is BASH). But apt-get is not a "shell command", whatever that might be. apt-get is simply a program, and more specifically it is package management software used under Debian related Linux distributions (like Ubuntu). Of course it is available to use under other Linux distributions.
So the reason it's not available for you to type in your terminal at work is simply because it is not present on a Mac. As others have mentioned Mac OS X does not follow the package distribution model as Linux does. You find those weird .dmg files or whatever Macs normally use to install applications. However there are similar distribution type systems available for Mac like MacPorts. Using Macports you follow a similar command interface to apt-get to install things
port install package
Follow MacPorts documentation for the rest.
Anything that is a shell built-in will be available under both Ubuntu/Mac (even moreso BASH specific things since they are the same shell), but the plethora of programs that you might expect in a Linux distro (i.e. coreutils and other GNU related stuff) is not going to be present.