What API do you want to install? Something like another mod API or MCP/Forge? Usually, every API has their own ways of installing (directly importing, maven, gradle). They should have instructions that will guide you.
There are indeed a bunch of different ways to install depending on the API. I am not sure on Botania specifically, but here is how to get CCC and NEI into your instance, if you want it. I know it helps out a bunch and will allow you to create a custom NEI recipes thing in the future if you have custom crafting, etc. I mean, the method MIGHT work with Botania, I'm not sure.