The first project I ever had a client for was my internship during my senior year of high school. My client had to calculate special grades called 'employability skills' for everyone at my school by hand. She hired me to build her a program that automated the entire process, there was also a requirement that the new automatic system had to be as similar to the old manual system as possible.
I broke the system down into 3 parts, based on the manual process that was already in place. I had to split a master excel sheet into many different sheets for each teacher, so that they could fill it out. Then I had to recompile all of those files back into 1 master file, and finally from the recompiled file, I had to calculate the grades for each student. I built the program in Java using csv libraries.
I was able to complete the project ahead of schedule, and even had time to add extra features like automatically emailing the teachers after the master file was split up.