Remove the floor trim all around the room using your pry bar and hammer. Don’t break it as you remove it. Set it aside.
Roll out a strip of plastic vapor barrier along the side of the floor where you want to start. Use a razor knife to cut the strip so the ends go up the sides of the wall by 2 or 3 inches.
Lay a floorboard at one end of the room, on the vapor barrier. Set spacers between the floorboard and the wall.
Snap a second board onto the end of the first one, pressing them until they click. Set additional boards end to end along the wall. Cut the final board on a miter saw to fit along the side wall.
Lay the second course alongside the first, snapping the boards together along their long sides. Arrange the boards so the ends don’t line up between the courses. Cut the last board as needed to fit.
Repeat, laying the courses side by side across the whole room. Continue staggering the boards as you lay them. Roll out more vapor barrier as necessary.
Cut the boards of the last course lengthwise, using a table saw, to fit along the ending wall with a one-half-inch gap left there.
Reinstall the trim using your trim nailer. The trim will hide the spaces around the perimeter.