When using configuration in Microsoft Azure websites, ensure that you put configuration that you are likely to change often in AppSettings. This allows you to make configuration changes in the Management portal of Azure rather than having to edit the web.config file directly. An example of where you might like to do this include settings that allow you to disable site features temporarily such as during an upgrade or routine maintenance.
App settings in the web config file are names/value pairs and are accessed as follows:
Which can be seen in the web.config as follows:
<add key="StevesSetting" value="Webconfig setting" />
In order to manage this configuration in the portal you need to navigate to your website and click the configure tab (in the old portal)
and scroll down to app settings, then add in the setting you wish to change
Or in the old portal navigate to the website and click settings then applications settings and scroll down to the app settings section