S-26 orignal formula milk for 2 week old

Hello everyone. My baby is 2 weeks old and i want to introduce formula milk because sometimes i have sore nipples and feel difficult to breastfeed so often nearly every 45 min. So i thought to use formula milk but don’t know about its preparation. According to instructions in 60 ml of water 1 scoop of formula should be mixed. But i dont know about the water. Like if i boil water then should i wait to cool it down for mixing the formula ? After preparation if my baby doesn’t finish it in one feeding can i use the left over ? Do i have to warm it again ? I am FTM please share whatever u think will be helpful. All advices are wecomed and thank you in advance😁