I think the website could be clearer, but the use case is already pretty clear: it's a foundational piece for you to build your own CI/CD infrastructure, it doesn't provide a complete experience out of the box. The first section says the following:

> Bob allows you to build your own custom CI / CD infrastructure thanks to it's composable architecture, allowing you to use Bob for various different purposes

The "Why" page goes further and explains what Bob is, so what is not described there, it doesn't ship with, like a UI, which would be up to you to decide which UI to use, or to write your own (or skip fully if you don't need it, maybe just use IRC/Matrix/Discord/Slack notifications?) https://bob-cd.github.io/pages/why-bob.html

> It feels like Bob CD website makes sense only if you already know how to use Bob CD.

Just as a disclosure; I have never heard about Bob CD since I read the linked website from this submission, so no previous experience. And I think I grok it pretty easily, although I've built and maintained more CI/CD integrations/platforms than I care to count at this point, so probably biased a bit.