First connect to your VPS using an SSH client like Putty.
If you are following directions on installing an application, it will typically give you the correct command like "yum install application"
If you don't know the application name, you can get a list using command: yum list | more OR yum list | grep applicationname
If you want to install phpMyAdmin for example but aren't sure of the application name.
You could find the name using command: yum list | grep Admin OR yum list | grep php
Either command will return any applications with Admin or php in their name.
The application name listed will end in .x86_64 which you will omit from the yum command.
For example you would use "yum install php" instead of "yum install php.x86_64"