One of the things you will find out pretty quickly if you stick with it is that "by the chart" is just a starting point.
There is one thing that really helped me "get" flash exposure; printing the main subject (the one lit by the flash unit) to look normal while completely ignoring the background.
This does three things;
1- it allows you to see that the subject can look normal when the flash is done well,
2- it allows you to see which way you need to adjust the chart, if the background is too dark the flash is too strong, and
3- it allows you to see how the direction of the light affects your subject. Get an extension cord for your flash and you can then move it off center and that will make a huge difference in how "normal" or "right" your subject looks, in the real world the light rarely comes from the camera's viewpoint and done well this eliminates the goofy outlining shadow on the wall.