Photo and Image Editing Software for Windows
My go-to app is GIMP – GNU Image Manipulation Program. It has functions similar to those found in Adobe® products and other high-end image editing software. As such, GIMP has a very steep learning curve.
This is the description on the web site:
The Free & Open Source Image Editor
GIMP is a cross-platform image editor available for GNU/Linux, OS X, Windows and more operating systems. It is free software, you can change its source code and distribute your changes.
Whether you are a graphic designer, photographer, illustrator, or scientist, GIMP provides you with sophisticated tools to get your job done. You can further enhance your productivity with GIMP thanks to many customization options and 3rd party plugins.
One of the features I use most is layers, which allows for the non-destructive modification of images. Think of layers as overlays, as found in computer aided design (CAD) software.
The online documentation on Layers can be found here:
A good way to visualize a GIMP image is as a stack of transparencies: in GIMP terminology, each individual transparency is called a layer. There is no limit, in principle, to the number of layers an image can have: only the amount of memory available on the system. It is not uncommon for advanced users to work with images containing dozens of layers.
The organization of layers in an image is shown by the Layers dialog, which is the second most important type of dialog window in GIMP, after the Main Toolbox. The appearance of the Layers dialog is shown in the adjoining illustration. How it works is described in detail in the Layers Dialog section, but we will touch on some aspects of it here, in relation to the layer properties that they display.
One of the plugins included with GIMP 2.8 is UFRaw which is used for processing RAW format photos. Each Digital Single Reflex Camera (DSLR) manufacturer has their unique RAW file extension that can be found in this Wikipedia article Raw image format, in the section Raw filename extensions and respective camera manufacturers.
I could go on and on about this, but there is so much online information, help and tutorials that anything I add would be redundant.