Go to the "Map" menu and click "Fractions". Here you can set the initial amount of gold for each player, and this is also where you change races if you want to battle orc vs orc for example. If you choose to edit a fraction you can change starting units in the reserve list, what units are available for purchase and so on. Very easy once you get the hang of it.
And to be able to deploy you must have units in the reserves list, which you don't have by default in MPM3, so you must buy some first in this case.