Here is the XO duties.
"As the Army Company XO, you run the day-to-day operations of the unit, along with the First Sergeant. Your primary responsibility is to assist the company commander in areas such as administration, supply and maintenance.

While serving as the Company XO, you will gain valuable experience working with the Supply Sergeant. You will learn about Physical Security and the Command Supply Discipline Program. You will also learn about inventories and property accountability. This will really help you out when you are one day a Company Commander.
In addition, as the Company XO, you will also get experience with administration. This could include writing NCOERs, OERs and awards. You will also oversee promotions, separations, schools, pay problems and so much more."