I expect that you're talking about FactoryTalk View, and the way that it integrates with ControlLogix tags.
FactoryTalk View can browse both online and offline ControlLogix tags.
To browse online, you must have RSLinx Enterprise configured to point a Shortcut to the controller, and of course the controller has to be running and loaded with a program.
To browse offline, you must still have RSLinx Enterprise configured to point a Shortcut to the controller, but the controller doesn't need to be connected to the network.
Instead, RSLinx Enterprise points to the *.ACD file and browses the tags that have been created inside that project file.
If a tag does't exist in the controller or in the project file, you can type in the tagname by hand wherever you choose to use it in FactoryTalk View.