..........- Neutral Density Filter: This will slow down how fast light comes into your lens,........
Well.......
technically..... it really won't slow down the light, at least not enough to make a difference in the field of photography. It will still enter the lens at 299,792,458 meters / 186,282 miles per second. There will just be
less of it.
Ah yes, but
technically that's the speed of light in a vacuum. When the light passes through other mediums... such as water or glass, it does actually slow down. Although ... when it gets to the open air on the
other side of the thin layer of glass in the filter, it speeds right back up again. But hey... it DID slow down the light for a scientifically measurable amount of time (even if it was very short lived.)
To the OP: When you say you "played" with or "fiddled" with the settings, I'm getting the impression that you're not actually confident what each setting does. You want to be confident that you understand what constitutes a correct exposure, what options you have to adjust and control the exposure, and why certain options work better than others depending on the type of shot you're taking.
Bryan Peterson's book "Understanding Exposure" is probably one of the more commonly recommended books for this, but there are others... including the Scott Kelby series (which I think is now up to 4 books.)
You can also use a filter to reduce the total amount of light. This changes your shooting circumstances.
A neutral density filter cuts the volume of light that can pass. In reality, less "photons" make it through the filter and into the sensor body than would otherwise have been delivered without the filter.
Sometimes they're sold in "stops" and sometimes in "density" values. Each "0.1" density represents 1/3rd of a stop. So an ND 0.9 would be a 3-stop filter (only 1/8th of original light passes through the filter.)
An outdoor photo on a sunny day (during mid-day) follows the "Sunny 16" rule. It says that assuming you don't own a light meter nor a camera with a built-in meter, you can assume that in full sun, you can set the camera to f/16 (the "16" in "Sunny 16") and then set the shutter speed to the inverse of the ISO. That means if you were using ISO 100, you could set the shutter speed to 1/100th. You would get a fairly accurate exposure with those settings. You could ALSO use any "equivalent" exposure. For example, you could open the aperture up by 1 full stop which results in double the amount of light getting through, but then use a faster shutter speed (such as 1/200th which is half as long as 1/100th) and you'd get the same total amount of light in the exposure. There are numerous options.