Start Managed Software Center (MSC) from the Applications folder in Finder, or through a search in Spotlight.
On the Front page in MSC you will find all available software that you can install.
You can navigate through the software available by using the Categories tab or find a specific app by doing a search in the upper right corner.
Once you have found the software you want to install, click Install under the icon of the software.
You can follow the installation process under the Updates tab, and also get an overview of what software that have an update available.