Setup for Newbie

Hi there!

I had some questions about set up. I have a freshly installed site with a few plugins. In the media settings, is there where I put the sizes of images for my theme when displayed on a regular PC screen?

Then once I upload an image or featured image for instance, will Retina plugin automatically make Retina versions? So I just go about things normally?

https://www.ads-software.com/plugins/wp-retina-2x/