Calculate Sales Items from a File

[Stressed]

Hi, I am writing the code for a final project, and I'm struggling with this portion. I honestly don't even know where to begin. It's a menu driven program. I've written everything else except for the portion that needs to pull from a file. I would really appreciate any help I can get. Thank you in advance! The directions are as follows:
In this component, you will calculate sales items from a file. The component will also calculate the sales tax, display a printout to the screen, and save the output to a file.
Needed:
1. Read sales items and their prices from a file.
-The name of the input file needs to be cost.txt.
2. Calculate the sales prices for each sales item.
3. Calculate the sales total.
4. Calculate the sales tax total.
5. Calculate the grand total.
6. The output must display all information.
7.Your program will also output to a second file.
-Must be named costout.txt