Your MEP 'Help' file is a good place to start. The first two entries in my version of MEP are 'Create still frame'.
It's not perfect logic, but frame s are under 'File' >> 'Export movie' >> Single frame a JPG...' with a shortcut of [Alt]+[N] -- [Alt+[M] for a BMP. There are options for resolutions other than the current project settings and also for inserting the frame directly into the current project.