The App Store adds applications to your desktop. Select an app, check its price and requirements, then download it. Wait for the download to finish before opening it. An app shown in the store is not automatically installed.
Free applications
Ninezilla is a file-transfer workspace. Choose an already connected server and see local and remote files side by side. Drag a file across to upload or download it, then follow the transfer in Task Manager. Opening a log or moving a file still requires the same permission as in Interwebs.
Rebel IRC provides public channels and private chat rooms. Download it, open it and choose your chat identity.
These app downloads currently do not reduce disk space. That does not make transferred files free of storage requirements: files downloaded through Ninezilla still need room on their destination disk.
Security subscriptions
Security Center and Sentinel use weekly subscriptions paid with game money. The store shows the modules, paying account, next payment and renewal status. Buying access, downloading the app and starting a service are separate steps.
The subscription belongs to the selected server. Stopping Sentinel does not cancel its subscription. After a disk reset you can download a paid app again without buying the same paid period twice; its expiry date keeps running.
Check the current store listing for available apps and prices. Premium membership is separate from these game-money subscriptions.