the tool for installing software on linux

All the installing tool command below need sudo access in order to use it.

Debian, Ubuntu: apt-get is the most common tool for installing software

apt-get update will update a local storage that stores the list of available packages for apt-get tool.
apt-get upgrade will upgrade all the packages that have patches or security updates to install.
apt-get install tomcat tab tab Will list all packages with name starts with “tomcat” available to for install
apt-get install tomcat6 will install the tomcat6 package.
apt-get remove tomcat6 will remove the tomcat6 if it is installed.

Fedora, Red Hat, CentOs: yum is the most common tool for installing software

yum update will update a local storage that stores the list of available packages for yum tool.
yum update ${packagename} will explicitly update a single package.
yum install ${packagename} will install the specified package.
yum remove ${packagename} will remove the specified package.

Mandriva: urpm is the most common tool for installing software

urpmi ${packagename} will install the specified package.
urpme ${packagename} will remove the specified package.