Yes, that’s all there is. Snap them on, add bands if you think they’ll be needed, then and start adding cables. See the section farther down on how to set the tension using the bands, but often they’re not needed.
IMPORTANT: Don’t spread the arms out too far! The more you bend them, and the more often you bend them, the more they will lose their “spring” over time. Yes, they can actually be spread quite large and they will “work” afterwards. But, never as well as before being over-stressed.