15 year old camera, cheap lens. Unfamiliar with ISO. Doesn’t do edits. Views 3″ images and then 24″ monitor. What could go wrong? They wonder why the images now look crap.
Here is my downvoted advice, to which I’ll add:
I do two or three things: I shoot first fully automatic, then I get a feel for the numbers if I’m not sure; otherwise I shoot manual – 1/200s, ISO 100~200 and f8 to get a feel for how much light there is. The image on the camera screen is usually only a lower-quality jpg. It will be processed. I usually shoot RAW anyway, just in case I want to edit differently to the jpg.
On my old 2010 era camera noise was an issue even at lower ISOs. The camera was rated upto 6400 but noisy after 800 even if the lighting seemed okay. Sometimes, too, even on my D5600 on auto, the camera screws up the ISO. Broad daylight at 12000 with timer set to 1/4000s… like why?
What software are you using to edit the RAW? Cameras are much better these days… just try to understand your camera’s real limits, not the absolute technical spec. limits – those are often optimistic.
Or are you just using this as a vehicle to show off your photos?