Can't udestandbase case N==0

#1

if we have to reach n=0 and we are at n=0 it should be 0 ways, Why it is 1 as describe by sir ??
and also f(n) = f(n-1) + f(n-2) + f(n-3) + 1
sir is not considering 1 why??

#2

Hi Rahul
You got it wrong.
We are talking about “how many ways to reach…”
So if i ask you in how many ways can you go from 2 to 3? You would say 1 way.
If I ask you in how many ways can you go from 2 to 2? You must say 1 way. How? You are already there, so take 0 steps. This is the only possible way.
I hope i am clear.