When someone asks you for a dua for a deceased , you can read this verse. It is just a reminder to yourself and others that everybody is mortal and will die one day.
Properly translated it means " We are for Allah and we will go back to him."
But it is not a duaa for maghfarat of a dead person. So please when someone asks you to pray for a deceased, please say a Duaa for maghfarat and grant of jannat for that person.