From VFXPedia

Tool Controls Introduction

Every tool added to a flow in Fusion has a set of parameters, or controls, that determines how that tool behaves. When that tool is selected, the controls for that tool appear in a window on the right side of the screen in the Controls Area. More than one tool can be selected at a time.

Each control window has a header. This is a small title bar for the window that displays the tool's name and a button to collapse or open the window. The control header is also a good place to access the tool's context menu.

Modifiers can also be attached to a tool's controls. Modifiers are tools like expressions, calculations, trackers and paths. When a modifier is connected to a control on a selected tool, its controls will also appear. These controls appear separately in their own modifiers tab for the controls window.