Which new item do I need to add in visual studio, so I can create a tool as demonstrated here where I can ask for user input before I run it?
I want the user to select a feature layer and then have drop down boxes populated with all available field names from that feature layer and they have to choose one field name.
You will need to create a Pro Dockpane for this.
There are a few examples in the community samples that illustrate this. The Create Sample uses layers and field selection in a dockpane: