Found this awesome code for pascal's triangle ... can someone explain it line by line to me?

Question

n=int(input("Enter number of rows: "))
a=[]
for i in range(n+1):
a.append([])
a[i].append(1)
for j in range(1,i):
a[i].append(a[i-1][j-1]+a[i-1][j])
if(n!=0):
a[i].append(1)
for i in range(n+1):
print(" "*((n+1)-i),end=" ",sep=" ")
for j in range(0,i+1):
print('{0:6}'.format(a[i][j]),end=" ",sep=" ")
print()

Answer 1

It is basically as follows:
put 1 in the line
while the line needs more numbers
add the two numbers from the previous line for the next number on this one.
if we need more than one number on this line
finish it with a 1