Functions help please

Question

Can someone explain this code to me please?

def func(x):
res = 0
for i in range(x):
res += i
return res
print(func(4))

Answer 1

res=0(you typed o)
for i in range(4)
i=0
res=0+0
i=1
res=0+1
i=2
res=1+2
i=3
res=3+3
6⃣