Like a lot of skills, learning photo editing is about familiarising yourself with the language and technique. Photo app Polarr put together an interactive guide that teaches you those concepts quickly.
Their guide includes a simple sliding animation for a number of effects ranging from exposure to Luminance. Each animation gives you an extreme example of the effect so you can really see it in action and learn what it does alongside a brief explanation of when you're likely use it. It's not going to make you an expert in photo editing, but it will lay down the basics so you can get started.
Newbie to Expert Photo Editing [Polarr]