Poor image quality

[Fletch]

Learning a new program is always a little frustrating.
Please follow the Quick Start Video Series linked in my signature - it will save you many hours of questions and frustration.

[massi-p]

I will study carefully the tutorials, just one last question:
if I understand it (I'm sorry but I'm Italian and I struggle with English technical) tell me to do a render smaller from 400x200 to be faster after ok .... but to increase the image, for example. 1400x800 would be grainy, due

[Fletch]

You are not understanding what I'm saying. You must make the HDR image which you are using to light your scene - the sky image. This image should be small, 400x200, so that the render engine doesn't have to calculate a lot of useless data.
Your image you are creating should be 1600px wide, or whatever you need. However, you should then replace the background sky in the image which you are creating with Twilight Render. See this tutorial: Subject: Background Image / Picture Using Alpha Mask

[KrisKar]

Im having similar issues with my renderings

Thanks for the support guys!