Could you please share some more information about the problem you are having? Could you share some screenshots showing what exactly is happening?
Also, is this happening only in 1 scene, or in any scene you try to render? How about a simple scene with just a box and a Corona light?
As to your question: rays per second is a unit telling you about your current rendering performance. Generally, the higher the number, the faster the rendering is progressing. Since Corona is a CPU-only renderer, the rendering process is done using the CPU, however this is a simplification because the overall rendering process requires communication between the CPU and the memory (and the hard drive, and other components, depending on what exactly you are doing...).
For more information, see:
https://support.chaos.com/hc/en-us/articles/4528225325713-Rays-per-second-too-low