Well, it's your homework, so I'm not going to give you the full code. Here are some pointers though:
1) Get the number of numbers the user is going to enter. If you don't know this, you don't know how big an array to allocate.
You will need: Console.ReadLine, int.Parse or int.TryParse - Google for them appending "MSDN" on the end.
2) Allocate the array.
int[] myArray = new int[numberOfNumbersTheUSerWillEnter];
3) You will need a loop to get the numbers.
for (int i = 0; i < numberOfNumbersTheUSerWillEnter; i++)
4) In the loop, read a number from the user as you did in (1) above, and stuff it into the appropriate array element:
myArray[i] = numberIJustGotFromTheUser;
5) Then use a second loop to write the numbers to a file.
6) Then read the numbers form the file, and print them to the console.
If you have a specific problem with any of this, feel free to ask. But don't expect us to write it for you - it's your homework, not ours!