Yeast is activated through the kneading process when making bread, as well as by the proving in a warm place which follows the kneading of bread dough.
There is no sugar in yeast because it is a living organism and living organisms don't need sugar.
Yeast will respire the sugar causing the yeast to give off Carbon Dioxide. Yeast will respire the sugar causing the yeast to give off Carbon Dioxide.
Might be old or the water is too cold to activate it or too hot and killed it.
Warm water and sugar.