If it's dried yeast you get a sterile glass and add some boiled cooled water(20c ish) and add the yeast . Leave it be for 10 mins and then give it a stir then after around 30 mins pitch into brew and give brew a good stir .
The dried yeasts I have used need to be rehydrated at a higher temperature than 20C - nearer 30C, but you should check the manufacturer's instructions as they vary. You don't have to rehydrate but you will kill half your yeast if you don't. I doubt it matters whether or not you stir if you just sprinkle. Again, follow the manufacturer's instructions.
