Please explain, I just do not understand

Question

Can you explain this code to me. I can’t understand how, when I type in the words hello, “Deja Vu” is displayed. It is not clear what each "for" line is responsible for.
Можно и на русском ответить.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SoloLearn
{
class Program
{
static void Main(string[] args)
{
string vvod = Convert.ToString(Console.ReadLine());
string result = "Unique";
for (int i = 0; i < vvod.Length; i++)
{
for (int j = 1; j < vvod.Length - i; j++)
{
if(vvod[i] == vvod[j + i])
{
result = "Deja Vu";
}
}
}
Console.Write(result);
}
}
}

Answer 1

Is it not your code?
This is for code coach problem..
Description you can find from link below clearly...
For loop check, if there is dublicates charecters in given input...
Test with Input:
abb
abc
https://www.sololearn.com/coach/54?ref=app

Answer 2

No, this is not mine. I can’t understand why i = 0, j = 1 and vvod [i] == vvod [i + j]

Answer 3

There should be actually j start from j=i+1.
Because if it atleast, one character dublicate charecter should be there to change result to "Deja vu".

Ex:
If input:
abcde
i=0 to 4
j=1 to 4-i
i, j : 0, 1 to 4, j+i=1+0= so 1 to 4
a!=b, a!=c, a!=d, a!=e
I, j : 1 , 1 to 3, in if I, j =>1, 2 & 1,3 b! =c, b!=d
Next I, j : 2, 1 to 4-2=2 so I, j =>2, 3, c!=d, c!=e
Next I, j: 3 , 1 to 4-3=1 so no comparison......
No further comparison...