As a part's unconnected port (shown by an X) comes close to a stationary port with which it is compatible, the dragged selection snaps so that those ports coincide.

Dragging automatically drags all connected parts. Hold down the Shift key before dragging in order to detach a part from the parts it is connected with.

Use the context menu on a part to rotate it. If it is connected with other parts, the whole collection rotates.