What is a picture editing software that is easy to use?

Photoshop

It will depend on what exactly do you want to achieve by editing the picture.

If you want to play with effects and add stickers to the photo, then PicsArt would be a good option for you.

If you are more into digital plastic surgery and want to edit your figure/facial traits, then you better use Photodiva portrait editor.

If you want to restore old pictures and remove all the scratches and stains from them, then you'll need Photoglory. It's a paid software but it has free trial version.

Of course, all these things could be done in multipurpose photo editors like Photoshop or Photoworks or Lightroom, but they are usually paid, too. Still, you can get a free trial version to see whether the software is worth paying for.