Hey, sorry about that I'll see if I can find a way to make it clearer.
Storage is the capacity to save production for future turns. For example, if you have 3 storage you can save 3 production for the next turn. If you have no storage then any leftover production is lost.
It is best used for gathering enough production for higher tier buildings or even wonders as you can combine part of one turn's production with the next turn's.