This is exercise number one. The goal here is to understand - in strictly pragmatic terms - how the meter (whatever that is, the details don't matter) in your camera behaves. As with all exercises, even if you think you know the answers, I suggest that you at least briskly whip through it. It may just take you a few minutes, if you really do know the stuff. Working through the necessary button presses and dial-clicks will prepare you for future exercises.
You're going to be adjusting the Aperture, Shutter Speed, and ISO settings of your camera. It doesn't matter what any of those words mean. If you're curious, there are a lot of resources on the Internet. Your camera's instruction manual probably has some information as well. I don't think it matters.
Set your camera on Manual Mode.
Figure out how to adjust each of these three settings, and figure out where the corresponding number is shown in the viewfinder or other displays in or on your camera.
Just make some adjustments at random and watch the numbers go up and down. Note where the limits are (eventually the number will stop changing, no matter how you click the wheel or press the button). All three settings will have a highest possible setting, and a lowest possible. They may be many many clicks apart.
Now point the camera at something. It hardly matters what. Continue making adjustments of Aperture, Shutter Speed, and ISO, but now watch what the meter is doing. It might be a double-sided bar graph, or a needle, or something else.
Whatever it is, it will be able to indicate "too high", "too low" and lastly "just right" somewhere between the first two. Don't worry about what "too high" or "too low" or "just right" actually mean. As a side note, "just right" isn't always right. It's just the camera's best guess. You can think of it as "the center" if you like.
Make adjustments to one control at a time, watching the meter, until you can get the meter centered on the "just right" position.
What's going on here is that the camera's meter has an idea of what a "correct" combination of these three settings will make a nice photo. There are many combinations that will work for the meter. Picking any one of the combinations will put the meter on the "just right" position.
Get the meter centered on "just right" and now adjust the Shutter Speed a couple of clicks one direction. The meter should change, and now indicate "too high" or "too low". Now adjust the Aperture a couple of clicks, until the meter goes back to "just right". You might have to back and fill a bit, since as you noted in Step 1, there are limits to how far each of the settings goes up and down.
The point here is that one setting can push the meter off of "just right" and another one can push it back.
Now do the same with each pair of settings. For example, change the ISO a couple clicks up and down, and try to correct by changing the Shutter Speed, and then by changing the Aperture. Any of the three settings can push the meter up or down, and then either of the other two can push the meter back to "just right".
At this point you should be able to get the meter in your camera to read "just right" in a variety of combinations of settings for Aperture, Shutter Speed, and ISO. These are the three settings called out in what is often called the Exposure Triangle, which you may look up at your leisure. There is a ton of technical detail, which is not really necessary to know, but which you may find helpful anyways.
If you stopped right here, you'd probably be able to take pretty OK pictures in Manual Mode.
But press on, I beg you!