Temper in south indian cooking means : Heat oil in a pan/ Kadai until it hot. If you drop the mustard seeds, it should pop immediately. Pop the mustard seeds until the last one. Otherwise it will be bitter. So make sure the oil to be hot as you drop the mustard seeds, it should pop (crackle) immediately. Then add the other items one by one and fry until golden. This will be happening soon, so keep everything ready to avoid burning. In North Indian cooking, just heat oil/ghee and add the whole spices and give it a fry.