pushthepayload.tv’s Winston Guide

Although this is an older guide and may be inaccurate regarding precise numbers, it's a wonderfully formatted guide with plenty of GIFs and images. Not only does the guide thoroughly explain concepts of playing Winston -- there are numerous visual examples, too.

Doc Sword’s Winston Guide

Although this is an older guide, much of its information is still good and still applies. A high-level introduction to playing Winston, covering his abilities in great depth. Doc Sword's guide covers not just "the numbers" -- but detailed information on how to use those abilities, too!