You don't have to use the terminal to install software in CentOS and most other Linux distributions. They commonly have a GUI-frontend for the software installation/uninstallation tool. This link will tell you more about the CentOS GUI software tool
Debian-based distros use aptitude and apt from the command line and the Synaptic Package Manager from the GUI.
At LQ, many persons will go right to telling questioners about command line tools because they are the lowest common denominator, while GUI tools might vary from distro to distro. This is especially likely with a distro intended primarily to be used as a server, such as CentOS and RHEL (Red Hat Enterprise Linux), because they are frequently installed without a GUI.
Slackware relies primarily on the command line, and Slackware does not resolve dependencies. Some of the Slackware-based distros, such as SalixOS, do resolve dependencies and provide a GUI package management tool.
Here are a couple of references that I have found particularly useful:
. It's oriented to Ubuntu, but it's full of good info.
. Machtelt Garrels's Intro to Linux.
You will find an overwhelming wealth of resources at The Linux Documentation Project