Basically just copy-pasted from the getting started page
Certus quartz buds will sprout from budding certus blocks, similar to amethyst. If you break a bud that is not finished growing, it will drop one Certus Quartz Dust, unchanged by fortune. If you break a fully grown cluster, it will drop four Certus Quartz Crystals, and fortune will increase this number.
There are 4 tiers of budding certus blocks: Flawless, Flawed, Chipped, and Damaged.
Every time a bud grows by another stage, the budding block has a chance to degrade by one tier, eventually turning into a plain certus quartz block. They can be repaired (and new budding blocks created) by throwing the budding block (or a certus quartz block) in water with one or more Charged Certus Quartz Crystal.
Flawless budding certus blocks will not degrade and will generate certus infinitely. However they cannot be crafted or moved with a pickaxe, even with silk touch. (they can be moved with spatial storage though)
By themselves, certus quartz buds grow very slowly. Luckily the Growth Accelerator massively accelerates this process when placed adjacent to the budding block. You should build a few of these as your first priority.
Harvesting the certus automatically is described here.