Hello,
I have made a new topic for your new questions.
If you are using a theme that features full width images then you should set your site image size to be that size or larger, ie, the width of the site.
For example 1366 is now a very common desktop monitor width, so you may want your large image to be that size or even larger.
For dimension, that is really up to you, in general, but, if you mean for a featured image header, they are usually panorama dimension, like 16×9 so image size size in pixels should be large, like 1400+ as I mentioned before.
Whatever you choose for your image sizes on your site, GD will always load responsive images for GD elements.
Are you having trouble with a particular image? Maybe we can advise.
https://wpgeodirectory.com/docs-v2/integrations/images/