how to do collision

I'm making a game where objects are falling down at the player and he has to dodge them but I don't know how to make collisions

here is my code

init = function()
  blockyY = -75
  blockyX = [-100,0,100]
  blockyI = 1
  currentX = 0
  i = 200
end

movement = function()
  if (keyboard.press.RIGHT and blockyI < blockyX.length -1) then
    blockyI += 1 
  elsif (keyboard.press.LEFT and blockyI > 0) then
    blockyI -= 1
  end
end

update = function()
  i -= 8
  if i <-200 then
    i = 200
    currentX = random.nextInt(3)
  end
  
  
  movement()
end

draw = function()
  screen.clear("white")
  screen.setLineWidth(5)
  screen.drawLine(-100,150,-100,-150,"red")
  screen.drawLine(0,150,0,-150,"red")
  screen.drawLine(100,150,100,-150,"red")
  screen.drawSprite("blocky",blockyX[blockyI],blockyY)
  screen.drawSprite("brick",blockyX[currentX],i)
end

ps. thanks to everyone who has helped me so far! I am new to coding and it means alot

Collision testing is just checking positions. To check if your objects are aligned on the x axis, test if currentX and blockyI are the same. To check if they are aligned on the y axis, test if i and blockyY are close to each other. Also, you might want to rename some variables so that they clearly represent a specific object and are conceptually similar. BrickX, BrickY, BlockyX, BlockyY, or something like that. It'll help you a lot as your code gets larger.

I tried that and nothing happened the blocks just go right through

here is my code

init = function()
  blockyY = -75
  blockyX = [-100,0,100]
  blockyI = 1
  currentX = 0
  i = 200
end

movement = function()
  if (keyboard.press.RIGHT and blockyI < blockyX.length -1) then
    blockyI += 1 
  elsif (keyboard.press.LEFT and blockyI > 0) then
    blockyI -= 1
  end
end

update = function()
  i -= 8
  if i <-200 then
    i = 200
    currentX = random.nextInt(3)
  end
  
  if currentX == blockyI and i == -60 then
    screen.clear()
  end
  
  movement()
end

draw = function()
  screen.clear("white")
  screen.setLineWidth(5)
  screen.drawLine(-100,150,-100,-150,"red")
  screen.drawLine(0,150,0,-150,"red")
  screen.drawLine(100,150,100,-150,"red")
  screen.drawSprite("blocky",blockyX[blockyI],blockyY)
  screen.drawSprite("brick",blockyX[currentX],i)
end

That would be because your brick moves 8 pixels at a time, so it is never at -60 y. Try -64. Better yet, instead of

i == -60

try:

abs(i - blockyY) < 16

That would trigger if the two are within 16 pixels. You can change it to whatever the size of your sprites are. That way, it'll trigger if the player moves into the brick from the side at the wrong time.

Also, you can't clear the screen in the update function, and even if you could it would only clear for 1/60 of a second. Try something more dramatic, like removing your player, not decrementing i anymore, or showing some text.