How movement was possible with this block of Code(If...Else)?

Hi I am Dheeraj and I have been learning Pygame through online websites and I had a problem. I am a total beginner and I wanted to know how the movement was possible through this block of code which is under If...Else. I have been trying to make this game - This is the full code -->

import pygame
pygame.init()
win = pygame.display.set_mode((1280, 720))
pygame.display.set_caption("Game of Squares")
bluex = 100
bluey = 100
redX = 300
redY = 300
bluevel = 6
redVel = 4
run = True

def drawGame():
     win.fill((0, 0, 0))
     pygame.draw.rect(win, (0, 0, 255), (bluex, bluey, 20, 20))
     pygame.draw.rect(win, (255, 0, 0), (redX, redY, 40, 40))
     pygame.display.update()

while run:
      pygame.time.delay(100)

      if redX < bluex - 10:
          redX = redX + redVel 
          drawGame() 
      elif redX > bluex + 10:
          drawGame()
          redX = redX - redVel
      elif redY < bluey - 10: 
          redY = redY + redVel 
      elif redY > bluey + 10:
          redY = redY - redVel
      else:
          run = False
      
      for event in pygame.event.get():
            if event.type == pygame.QUIT:
                  run = False

      keys = pygame.key.get_pressed()

      *if keys[pygame.K_LEFT]:
            bluex -= bluevel

      if keys[pygame.K_RIGHT]:
            bluex += bluevel
      
      if keys[pygame.K_UP]:
            bluey -= bluevel
      
      if keys[pygame.K_DOWN]:
            bluey += bluevel**
      
      drawGame()
          
pygame.quit()  

This is the block of code which is been used here for movement -

if redX < bluex - 10:
          redX = redX + redVel 
          drawGame() 
      elif redX > bluex + 10:
          drawGame()
          redX = redX - redVel
      elif redY < bluey - 10: 
          redY = redY + redVel 
      elif redY > bluey + 10:
          redY = redY - redVel
      else:
          run = False

So can anybody pls tell how this is possible and explain this block of code. And how 10 came here. Pls, tell me ASAP.