For windows machines only. Sorry Mac Lovers!
We are providing a safe direct link to the real Paint.net download site. There are many sites that provide this download, never use them Trust me I learned this the hard way.
Use this to get to the download page 
If you need support and information for Paint.net here is a link to the forum site. Paint.net Forums
There are some plugins to do some more complex things on Paint.net I will provide you with the direct links to the best plugin pack pages.
BoltBait's Plugin Pack
Pyrochild plugins
The above plugins have an auto installer now. But if you would like to install one of the many other plugins on the paint.net site that needs to be manually installed. Below Sheryl has made a video explaining how to . This same video can be used to uninstall plugins if you would like to delete a plugin also.
After Viewing the instillation video there is a playlist of How-to videos for Paint.net that Sheryl has produced. You can find the Paint.net Tutorials on Youtube and it will give you an idea of just how easy this image editing tool is to use!
Enjoy!