Also, to add to what Jo said, there is (unfortunately) no... er... "quality control" when it comes to the online library. There's a lot of chaffe amongst the wheat, so to speak. Many of the public components are custom code block cut-n-pastes from places like bootsnip.com, so often, unless you're familiar with coding, you'll have trouble styling or customizing downloaded components. Also keep your eye on the bootstrap version. There are a bunch of components from BS 3.x that don't always work correctly with 4.x sites.
I've only uploaded a few blocks, but I always put very clear instructions in them on how to customize and whether they require any code knowledge. I try to stick to creating components that don't require custom code. I have nothing against custom code, and use it a lot, but I know a lot of people who use BSS do not.