A few changes I did in tile.py was I added color to my draw_tile() function and added a sqwiggle to make my tile unique. This made a cross pattern tile with a sqwiggle inside the tile.

Checkpoint 3:
When writing my own programs I think I would try to use docstrings more. When writing programs I normally use the hashtag which has become muscle memory for me but I will try to use docstring because it looks cleaner and more effective.

tile.py

@@ -2,8 +2,20 @@ from turtle import *
 
 def draw_tile(size):
     "Draws one tile, which can be repeated to form a pattern."
+    
     draw_tile_outline(size)
     draw_squiggle(size)
+    pencolor("red")
+    forward(size/2)
+    left(90)
+    forward(size)
+    backward(size/2)
+    left(90)
+    forward(size/2)
+    backward(size)
+    left(90)
+
+    
 
 def draw_tile_outline(size):
     pencolor("#dddddd")
@@ -42,3 +54,6 @@ def quarter_arc_right(radius):
 def quarter_arc_left(radius):
     "Draws a quarter of an arc, turning to the left."
     circle(radius, 90)
+
+draw_tile(100)
+done()

tile_grid.py

@@ -10,7 +10,7 @@ from tile import fly
 def draw_tile_grid(width, height, tile_size, tile_function):
     """Draws a (width x height) grid, with tile_function drawn on each tile.
 
-    (Your explanation here.)
+    The draw_tile_grid function draws a grid of tiles by repeatedly calling a given tile-drawing function across each row and column, moving the turtle to the correct position after each tile and row until the whole grid is complete.
     """
     for y in range(height):
         for x in range(width):