An “Extension” is like an Add-on for Revit if you are familiar with that. It’s a way for anyone (Our team, or other users both create them) to
Extend Dynamo; basically creating new functionality or modifying existing functionality.
For example, @john_pierson has the Monocle View Extension that adds new annotative functionality to the workspace: Alignment icons in canvas, easy way to create groups, custom colour etc.
@Mostafa_El_Ayoubi has the DynaMaps View Extension that creates a connection to a series of resources (Open Street Maps, Topographical repositories etc.) to allow you to quickly and rather effortlessly bring in site context data to your Dynamo workspace; roads, buildings, trees etc.
In your case, you could create a View Extension (As per @JacobSmall 's suggestion) to allow you to
inject values into the out-of-the-box Number Sliders. This may allow you to get what you are looking for!