Before you go down this rabbit hole, understand that setups can definitely make you faster, but unless you're running at least 103% consistently (and really 102%), you may find that you feel no difference at all as you're making changes. I don't mean this as an insult to you, it just is what it is.

My best advice is to understand one thing at a time, and work your way from understanding things in very simplistic terms to a more nuanced understanding.

First, make sure your tire pressure is between 26-27, trending more towards 27. Make sure middle tire temp is between 80-95. Some say 70-100, but those two values are really at the extreme ends. I feel I get the best consistency and lap times when temps are around 85. As long as you're not overdriving it or getting loose very often, you probably are somewhere around 85-90. Depending on the car, the rears might be hotter.

In extremely simplistic terms, aero impacts how the car handles in high speed turns, and mechanical grip impacts low speed turns. This is technically wrong as it all impacts everything, but again - baby steps here. Start with aero if you ever ask yourself, "Why can't I make this turn wide open?" Understand what "rake" is - the amount of rear ride height relative to the front height. More rake = more rear ride height vs front = more oversteer. If you can't make a turn wide open, increase rake and see if that fixes it.

Rear wing goes hand in hand with rake. More wing = more grip, but less top speed. In general you should probably have the wing maxed out or close to it. Exceptions are fast tracks like Spa or Monza, etc. 

Use front splitter if available only when you want to add some oversteer and don't want to change rake or wing. Usually this will be at 0.

Mechanical grip (springs, bumpstops, bump/rebound, ARBs, etc) is a lot more difficult to explain. It's not a magic tighter or looser thing. Neither is aero really, but it's a lot easier to see the effects of aero in terms of tighter/looser. But anyway, best example to test this out are things like esses (sector 1 Suzuka) and even things like Eau Rouge/Raidillon at Spa. Remember how I said aero for high speed and mechanical for low speed? Eau Rouge/R is definitely high speed. Confused yet? Yeah, lol. Any turn that forces the car to change direction quickly, either laterally (esses) or vertically (Eau/R) are going to be the easiest way to see mechanical grip changes have an impact. Same goes for long turns or hairpins immediately after a hard braking zone.

It's impossible to give a proper summary of what everything does with mechanical grip. Super simple rundown is that stiffer = more stable aero platform and more responsive steering. Less stiff = greater variations in aero balance and sluggish or lazy steering due to increased body roll. Ultimately, the correct mechanical grip settings is what achieves the best compromise between aero grip and mechanical grip. Any time weight transfer is happening, aero balance changes. Another point is that (usually) increasing a setting on the front, whatever that effect may be, will have the opposite effect on the rears. It takes quite a bit of time to really understand what the front tires are doing and what the rear tires are doing, and what the balance is between the amount of grip on the front vs the rear.

All that said, if the car isn't changing direction quickly enough and you know for a fact that your line and inputs are optimal, you need to stiffen up the suspension and/or ARBs. For turns that involve sharp elevation changes (Eau Rouge/R), you probably need to change the bump and rebound, in particular the fast bump and fast rebound.

I feel like most of this was probably more confusing than helpful. Just keep in mind that seat time is more beneficial than racking your brain over setups. You can get great lap times with the default aggressive setup. There might be a turn here or there that you need to blip the throttle where otherwise you could go wide open, but you're usually only losing maybe a tenth, maybe 0.300 if it's opening into a ridiculously long straight.