How do I use python to display information on PiScreen?

You will need to use the pygame module to display information on PiScreen with Python.

And before you call pygame.init(), you need to set the environment variable to point the output to PiScreen. (/dev/fb1).

Example code;

import pygame, sys, os
from pygame.locals import *
os.putenv('SDL_FBDEV', '/dev/fb1')
pygame.init()

# set up the window
DISPLAYSURF = pygame.display.set_mode((480, 320))


# set up the colors
BLACK = (  0,   0,   0)
WHITE = (255, 255, 255)
RED   = (255,   0,   0)
GREEN = (  0, 255,   0)
BLUE  = (  0,   0, 255)

# draw on the surface object
DISPLAYSURF.fill(WHITE)
pygame.draw.polygon(DISPLAYSURF, GREEN, ((146, 0), (291, 106), (236, 277), (56, 277), (0, 106)))
pygame.draw.line(DISPLAYSURF, BLUE, (60, 60), (120, 60), 4)
pygame.draw.line(DISPLAYSURF, BLUE, (120, 60), (60, 120))
pygame.draw.line(DISPLAYSURF, BLUE, (60, 120), (120, 120), 4)
pygame.draw.circle(DISPLAYSURF, BLUE, (300, 50), 20, 0)
pygame.draw.ellipse(DISPLAYSURF, RED, (300, 200, 40, 80), 1)
pygame.draw.rect(DISPLAYSURF, RED, (200, 150, 100, 50))

pixObj = pygame.PixelArray(DISPLAYSURF)
pixObj[380][280] = BLACK
pixObj[382][282] = BLACK
pixObj[384][284] = BLACK
pixObj[386][286] = BLACK
pixObj[388][288] = BLACK
del pixObj
# run the game loop
while True:
    for event in pygame.event.get():
            if event.type == QUIT:
                        pygame.quit()
                        sys.exit()
    pygame.display.update()