Composer has a very simple set of terminal commands that lead you through the process of installation. Occasionally (and more frequently for windows machines) there are configuration files that need to be modified in order for Composer to work correctly. If you're asked to make configuration changes take it one step at a time, and feel free to ask your teacher for help.
Just follow along here to get Composer.
In order that the applications we build behave the same way on personal computers as Epicodus machines, you'll need to make sure your local PHP version is updated. PHP 5.6.27 is the version we use at Epicodus but the last number (called a minor version number) is not as important.
In the terminal from any directory run:
$ php -v
You should see something like this:
PHP 5.6.27 (cli) (built: Apr 14 2016 09:39:35) Copyright (c) 1997-2016 The PHP Group Zend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies
If the version number right after PHP on the first line is lower than 5.6.0 you'll need to update.
This tutorial has very clear step-by-step directions on how to achieve this along with descriptions of why we run commands and what errors might arise. Follow along there, and if a problem arises feel free to ask your teacher to help.