How do you dissolve yeast in warm water?

Warm, but not hot water (between room temperature and 100 degrees fahrenheit) can be used to dissolve yeast; chefs should be careful to avoid adding too-hot or too-cold water, or the yeast could either remain dormant or die and fail to cause rising. Dissolving yeast in warm water is a way to wake and activate the yeast before it's added to dough.

Yeast is a living organism, and it is dried to make it shelf stable. Activating yeast in some hot water prior to use is not necessary, but adding warm water and some sugar to the yeast can be a way to tell if it is still good for use or not.