There is no equivalent to apt-get on OSX: Installs are generally graphically based and you need to download the installers from the web.
PHP and Apache 2 are already included in OSX out of the box. Apache 2 is turned on and off using the "sharing" system preference (turn on Web Sharing). The config file for Apache is located in /etc/apache2/httpd.conf (turn web sharing off and back on to apply changes). By default, apache isn't configured to include the php or fast-cgi modules, but the configs are present (and commented out) in the httpd.conf file so configuring them is trivial
OS X makes a very capable alternative to the LAMP platform and once you get used to the differences, you should be pretty comfortable coming from a Linux background
The closest thing you'll get to apt-get is apple's app store. Its not command line like apt-get (but then ubuntu has been moving people away from the CLI and apt-get anyways) and it allows you to download and install applications.