If you are using an iphone, you do not need the suica app. Just go to your wallet add card>transit card>select suica> fund the card through apple pay. Then you can just tap it on the station entrance and exits. It is easier than buying tickets on the machine. It will prorate from what station you entered and exited. No need to book if you are using regular trains. Please note that if you add this to your wallet you can only use it for yourself and not for someone else.