Paint.NET is a fairly lightweight and simple free graphics editor, that’s probably one of the easiest to learn how to use. It has plug-in and multiple layer support as well as a fairly wide range of tools and filters to help you modify your images, and the software is suitable for both graphics editing and photo retouching.
You can find plugins on the GetPaint.NET forum and there’s also a plugin pack called the BoltBait Pack which you can download for free from BoltBait.com.
That being said, its core features fall short in some respects. For example, it has no point-to-point selection tool that even Microsoft Paint has nowadays and it does not have very good vector support by default, although there are plug-ins for that. Paint.NET is also only available for Windows.
Basically if you don’t really need any advanced graphics or photo editing features, or if you’re a beginner in terms of graphics editing, then Paint.NET is a fairly good program to start off with. If you have an older computer, it may be a good choice as well because it will likely work a bit smoother than some of the other newer free graphics editors.
Also, I have made a basic photo editing tutorial for Paint.NET, check it out to learn the basics!
Multiple layer and limited vector support.
Selection tool, but no point-to-point selection.
Lightweight and simple interface.
Tools and filters for both basic and intermediate photo retouching and graphics editing.