I had a lot of trouble wrapping my head around settings for a long time, but I finally go it sorted by thinking of it as a continuum.
First, you have three variables that you are working with: shutter speed, aperture, and ISO. Each one comes with trade offs-- too low a shutter speed and you'll get blurring from shake, too small an aperture number and you might not have enough depth, too high and you might have too much, and too high an ISO and you may have to deal with grain.
So given that every setting has trade offs, you naturally want to figure out a way to balance each one, but first we'll go back to the continuum.
Suppose you have a scene, with a fixed level of light, which we'll call Y. There are lots of ways to approach how to expose for the scene, it's all about what's important to you. In this case, we'll say that it's a very sunny day. Here's a couple possible exposures.
If you shift the ISO around, you can either change the f/stop or the shutter speed
ISO100, f/16, 1/100
ISO200, f/16, 1/200
or
ISO200, f/22, 1/100
If you shift the aperture around, you can change either, but we'll leave the ISO at 100
f/16, 1/100
or
f/11, 1/200
or
f/2.8, 1/2000
All of those would give you the same exposure, but with different depth of field. Obviously, you can look at it the other way as well, and change the shutter speed to suit what aperture you are looking for.
Every time you change by one stop (your camera is probably set in 1/3 increments, so every three clicks), you double or halve the amount of brightness. Which means that if you think the scene is too bright or dark, you would change one variable, whereas if it has not change, then you need to change another variable to compensate for your change.
I'm not sure this is making sense, so keep asking questions. It's a bit tough to wrap your head around at first. Try thinking of the different options as shifting dials, or as equations if you are a math person (something along the lines of A+B+C=Y, --- if Y=10, it could be 1+1+8 or 4+4+2 etc etc).