Unable to understand code Matplotlib for loop with range

Hi there,
please help me understand the below code block. I am unable to connect how i and range is connecting to other variables in block.

fig = plt.figure(figsize=(12,12))

for i in range(5):
ax = fig.add_subplot(5,1,i+1)
start_index = i*12
end_index = (i+1)*12
subset = unrate[start_index:end_index]
ax.plot(subset[‘DATE’], subset[‘VALUE’])

plt.show()

Please try to provide the mission link.