There’s going to be a learning curve, and it’s going to involve a lot of Google searches. Experience with software like Photoshop won’t help much, because GIMP does things its own way, and expects users to figure those ways out on their own. You just need to find those tools, and figure out how they work. You can customize the user interface, putting tools you use regularly front-and-center and burying the tools you don’t. This layer-based editor supports most file formats, and has all of the tools you need to touch up photos: adjustments for things like color balance and contrast, yes, but also filters and simple drawing tools. In terms of features and flexibility, open source stalwart GIMP is the best free Mac image editor you can find. GIMP: Feature Complete With a Steep Learning Curve
