This action assumes you know what the filename is. The various GUIs should have a similar Load action where the filename is optional, and will provide their own file selection mechanism to let you choose the file name.

Arguments:

Layout Loads an entire PCB layout, replacing the current one.
LayoutToBuffer Loads an entire PCB layout to the paste buffer.
ElementToBuffer Loads the given footprint file into the paste buffer. Footprint files contain only a single subcircuit definition in one of the various supported file formats.
Netlist Loads a new netlist, replacing any current netlist.
Revert Re-loads the current layout from its disk file, reverting any changes you may have made.