When I last used it (Aug 2020) seemed like they were trying to evolve out of a stricter build/test/release flow, like Travis, and into a looser/more general workflow system, like CircleCI. At that point, it felt like the workflows were a bit half-baked – getting caching right between workflow steps so that you could build a performant pipeline that didn't repeat unnecessary work was tricky if I remember correctly.
Apart from feeling like they were in that sort of transition, GitLab's docs were fine, better than Circle's, but I find GitHub Actions much clearer.