Storing Mana simple, as long as you have at least 1 Mana Pool you are ready to start generating Mana. Initially generating Mana will cost you a few resources but as you progress further into Botania you will be able to generate Mana more efficiently and automation becomes much easier. If you have access to other mods then automation is far simpler.
As you first start playing around with Botania there are a few options to get you started with generating Mana. These Mana generating Flora can be crafted within the Petal Apothecary with a few petals, later on, flowers require more and more materials which need Mana to be crafted.