There are tons of tutorials online, including on Youtube. Here's our page with lots of useful learning links.
Photoshop is expensive but very commonly used. Elements is its simpler, much cheaper sibling. Many photographers just use Lightroom. Affinity Photo is cheap and very similar to Photoshop.
Edit with the RAW editor before switching to the full editor.
Learn to use selection, layers and blending. It takes effort, but it's worth it.
A lot of editing is 'select and adjust'. Select an area, subject, tone, etc. then adjust it (colour, tone, gradient, etc).
Check digital images very carefully, with the 'eye of the judge' before you print them. Then look at them again in print form.
Consider adding a two pixel white border to projected images (some judges like them).
Check that there is detail in both the shadows and highlights.
Perhaps the most commented-on item by judges is cropping, where they often suggest an even tighter crop. Look for the better picture within your picture.
Here are a whole set of links to useful articles, web pages, etc.
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