Property bags are explained in another article: Property Bags in SharePoint 2013 – Store, Retrieve Custom Configurations, In short: The property bag feature provides a convenient way to store and retrieve custom configurations, instead of having to store them in web.config files.
Usually, property bag settings are managed programmatically with SharePoint object model code in C# ow with PowerShell. There is no user interface to view/add/edit/delete the property bags key-value, but SharePoint designer can be utilized to manage property bag settings in SharePoint at the site level. Here is how:
- Open your SharePoint site collection with SharePoint Designer
- Click on the Site Options button from the top right hand corner of the ribbon
- You’ll be presented with a window to manage site’s property bag under “Parameters” tab.
- From here, you can add, modify or delete properties.
In SharePoint 2007, It’s under: Site >> Site Settings >> Parameters tab!