HI DeDiary , on your screenshot you have the default package, which includes All SysApps (they can't be removed) and only a few of CoreApps. You can download other CoreApps (like Posts, Discussions, etc) for free. 

Key&Secret is, in fact, free and you can generate it here -  https://una.io/page/kands-manage - it is used to link your site with UNA.IO to be able to download those apps directly from within UNA Studio and to update them later. This connection is securely established via oAuth2 protocol REST API.