GIMP has functionality similar to Adobe PhotoShop. It will present a complex learning curve similar to PS. If you don't like it / can't 'get' it in terms of effective usage, at least you didn't pay too. Recognize GIMP is freeware 'as is' software. There may be a community of users willing to help, but no one you can turn to directly for help such as you can obtain for commercial software.

As you consider any candidate software, consider the trial period offer for each candidate software. Use one-at-a-time for the entire trial period, including the available training, possibly always against the same set of 20 to 100 images. Make an informed decision that hopefully gets it right the first time. Consider the online documentation and free video training (u-tube) in the context of your trial-period comparisons.

Utube is a great source of information for any / all digital editing software. Don't waste money on training until you've exhausted all the free options, either from the vendor's site via your purchase (or subscription) or from Utube.

I know you're asking about free programs, but consider whether you could afford the $10/month Adobe Photographer's plan. For that you get Lightroom, Lightroom Classic, and Photoshop, as well as a free web site to display your photos. If you go the Adobe route, I'd suggest you start with Lightroom or Lightroom Classic (I use the latter). If you later decide you really like photo editing, you can explore the much more complex Photoshop in the future. It's pretty easy to get to the level of basic competence with Lightroom Classic. I've looked at Gimp, and found it nearly as complex as Photoshop.