The Node Editor and modifier conventions
Fusion's core workflow is node-based: every effect is a node connected into a tree in the Node Editor, and most of the shortcuts below either navigate that tree or manipulate the selected node(s). Cmd (Mac) and Ctrl (Windows, Linux) are interchangeable for the same action throughout Fusion, since it's the same cross-platform codebase behind DaVinci Resolve.
A second layer of shortcuts is scoped to whichever panel currently has focus: Cmd+F fits the image in a viewer, opens the Find dialog in the Node Editor, and fits splines to the window in the Spline Editor, depending on which one you last clicked.