Press P during game play to display a list of
countries and items from that country. Choose your country (for
example, if you are playing as France select the country France)
from the right side of the list. This will bring up a new list
on the right side, with people and buildings from your country.
Choose what you want to build (for example, King's Musketeers)
from the right side and click on the button on the bottom-left
corner. The button looks like a word in a different language.
This will take you off the list screen and back to the game. When
you left-click the mouse you will be able to build multiple duplicates
of what you selected. To build the duplicates you mist have the
correct resources. To get it to where you can select troops instead
of make them, just P again, select your country, and press
that same button you pressed in the bottom-left corner.