Couple of things:
1) It is a very good idea to do several runs of the Windows Speech Recognition (CTRL panel) first. The more you do it the more accurate it gets and the better commands you will be able to use in VA
2) You can completely manually set up VA if you prefer: As @Arimus says, most controls from the HOTAS will be keybound also. If you go to VA profile, you can then edit things in the panel, which also means you can add time delays, multiple keystrokes, macros etc. Therefore for example you could create macro for max shields which, in order, presses down key (default for balance power) then pushes right key three times. You type something like "Shields Up" (without quotes) into the VA bar at the top of the command, and presto, when you say Shields up it will execute that command.
Quite a popular one I use is the "Run" voice command. This simultaneously retracts hardpoints, fires chaff @ 10 second intervals, balances power to shields and engines, boosts engines every 10 seconds and commences FSD charge. All I need to do is steer!
Enjoy!