Can someone explain the following code below?

I'm not certain what's going on in this code and how the output came to be [1, 3, 6, 10, 15]

Code

lst = [1, 2, 3, 4, 5]

lst_2 = []

add = 0

for number in lst:

add += number

lst_2.append(add)

print(lst_2)

Answer:

[1, 3, 6, 10, 15]