For finger drills and learning the keys on the steno keyboard, you'll want to make Plover send the raw output instead of translating it into words. To do this, show Plover's main window (PHROBGS is the usual chord for this, or there should be an icon in the task bar). Then un-check the checkboxes next to main.json and user.json to turn them off temporarily.

Alternatively, you can open the Plugins Manager from the Plover main window and install the plover_dict_commands plugin. You may need to restart Plover after installing the plugin? Not sure about that.

Define a dictionary entry to switch to raw steno: maybe in commands.json. I think many people use RA*U as {PLOVER:solo_dict:+commands.json}. This will ensure that commands.json is enabled, and will disable all other dictionaries. Then you'll need a definition to enable your dictionaries again. The command for this is {PLOVER:end_solo_dict}.

Personally I do this slightly differently: I have a special dictionary return-from-raw.json (which I put at the very bottom of the dictionary list) with the following contents:

{
	"RA*U": "{PLOVER:end_solo_dict}",
	"R-R": "{^~|\n^}",
	"STK-G": "{#right}"
}

Then my normal RA*U command is {PLOVER:solo_dict:+return-from-raw.json}. So I can use RA*U to toggle raw-mode on and off, and in raw mode I only have Return (which you press three times to repeat an exercise in Steno Grade) and the right arrow (which randomly generates a new exercise).