The full key/mouse reference. For the "why" behind these, see Graph Navigation.
They sit next to each other under your left hand and spell out the thing they switch. Neither fires while you're typing, so a u in the middle of a sentence stays a u. See Space Studio and Publisher Studio: Basics.
Ctrl+Tab flips to the other studio from either one, and it works while you are typing too.
With a node selected:
Select two nodes and the shortest route between them lights up while everything else dims. Nothing disappears and the camera stays where it is. Select one node and Pathfinder asks for the other end. Select none and you click a start, then an end. A strip along the top names each stop and connector on the way, and closing it (or pressing R again with nothing selected) clears the route. More in Pathfinder.
Connectors: select connector(s), click a connector type in the left panel, or click the change-connector-type button in the bottom bar.
Nodes: select a node in the right panel and drag it into a new category, or click the change-node-type button in the bottom bar.
We deliberately avoid reinventing these, your machine already does them well.
Filamental runs on macOS, and everything above works there. Where a keyboard shortcut uses Ctrl, Cmd works too, since the app accepts either. The single-key shortcuts (U, I, O, P, T, G, 1-4) are identical on every platform.
The mouse and trackpad gestures are the one exception: Ctrl+drag for marquee select is Ctrl everywhere, Mac included.
Still stuck? Email support@filamental.space.