Getting fluent at using ANY of these complex programs is difficult and takes time and experience
"adjusting colour levels and contrast, etc to get the best out of your photos or manipulating the image by removing/modifying/adding the content?"
Spare a thought for GIMP, originally written for Linux and then ported to Windows. Free, with regular updates and add-ons.
Interface is no less complex than Photoshop, but once you have learned some Photoshop it is hard to change.
(there IS a port that makes GIMP more Photoshop-like)
If I Could Do It All Over Again I'd really learn GIMP and forget Photoshop thereby saving $$$$ - but YMV
Mac