Rendering problem, or?

Hello dear Community,

I recently started using the program, and unfortunately, I have a problem.

I'm not exactly sure what the problem is and how to fix it, but I'll attach photos to make it easier to understand. When I put together the scene in the design section, everything looked perfect, but when I started rendering, problems began. The final photo is unclear; grainy reflections are everywhere, and the colors are not as beautiful as in the preview.

What can I do to improve the final product? Which options did I click wrongly?