Rendering a part is the last step for a final product. If you want to make a real look for your part, you should use this feature of CATIA application.
The rendering time of a part or assembly is different depending to the settings and quality do you choose. For example, if you want to have a high-resolution render of your part, the time will be longer, and if you want a fast rendering you should use low resolution and medium or low quality.
You can choose the source light, the number of sources or the type. Also, you can change the background color, or image by uploading a new background image. For example, if you want to see how looks your part on a table, you can take a photo of the table, upload this in your PC and put it in the background. Look for the light source and edit the light direction to have same shadows. This tip, works very well when you want to create a catalog.
For a real look, you can change the view of your part from parallel to perspective.
At the end of rendering, you can export the result using a large type of formats like (.tiff, .png, .jpg, and more). Personally, I use .jpg at high quality.