Try this:
static void Main(string[] args)
{
string inp = Console.ReadLine();
for (int i = 0; i < 5; i++)
{
Console.WriteLine("{0}, {1}", inp, i + 1);
}
}
ReadLine returns a string, not an integer, so you need to store it correctly. The variable you store the string in, shouldn't be the same name as your loop variable, or the system won't know which one you mean!
WriteLine can take a format string as its first parameter which describes what to print. In this case it says "print the first variable, a comma, then the second variable".
So the result of the loop (assuming you entered "Hello") would be:
Hello, 1
Hello, 2
Hello, 3
Hello, 4
Hello, 5