Yes, lots of good advice. Lots to read.
You need to teach yourself how to judge exposure. Here's how I was taught. And this is for general exposures ( no studio lights or flashes ).
Use the aperture for what you're shooting, use the shutter for light.
So, if you're shooting a single object, you know you want shallow depth of field so F2 / F4. Put your aperture at F4 and starting shooting, adjusting the shutter between shots , faster or slower to get the exposure. If the shutter is too slow that you're blurring, this is where you UP the ISO. Start at 200. You'll hit a point, you take a shot, and you'll KNOW right away what to do to fix it.
An easy practice for this is set up something on a table / desk in good light. Shoot for depth of field. F4 and take what you think is the proper shutter. Go from there, it'll come to you quick
If you're shooting a landscape, you want it all in focus so F8 and higher. Same ISO or lower unless you're doing astrophotography.
Higher ISO's, yes will boost the exposure, but it will show noise in the underexposed sections of the image, and spots of high contrast. Low ISO's only if you're doing landscapes
Good luck, and have fun and don't spend more time reading than shooting, takes the fun out of the learning part
