How to install Composer on Debian / Ubuntu LinuxnixCraft

I'm trying to upgrade my Mediawiki installation and I'm getting an error that read as follows:     Error: your composer.lock file is not up to date, run "composer update" to install newer dependencies How do I install composer command for my PHP installation on Debian or Ubuntu Linux running LAMP or LEMP stack? How do I Install and use Composer on running Ubuntu Linux server and fix this problem for mediawiki installation and/or manage and install PHP packages and dependencies for my project?