To get started with Botania, you need to have done enough Witchery to get Mutandis.
With this you can get a Petal Apothecary, which allows you the get a Pure Daisy.
The Pure Daisy can be used to get Livingrock and Livingwood. Those are required for mana storage and transport.
The final thing you will want to get is a thermalily, and then you can get to producing mana.

Do note that you while you can craft the passive generating flowers, like the daybloom and the nightshade, they rapidly decay into dead bushes and are next to useless for mana production.
They are still enabled to serve as fuel for a Rafflowsia.

Your goal for now is to acquire some Manasteel and Mana Diamonds, as crafting runes is gated behind Blood Magic.