You've just reworded this sentence from when it was referring to a kernel. It made sense then, but its combination with the sentence about stopping the notebook server was confusing. Now it seems a bit redundant, and you don't mention the kernel at all.

There are three separate things that you can close or stop:
- Closing the browser tab where you're editing the notebook
- Stopping the kernel associated with that particular notebook
- Stopping the notebook server, which will stop all kernels, and prevent loading or saving any notebooks.