It's the best thing ever. It makes you scale, scew and rotate the selected area!
For example if you drew an eye too big, you can just select it and press control T to adjust it. It's the BEST thing about digital arts imo.
Getting better at digital art is mostly trying and seeing what all tools do. And thinking what you could use the tools for. Just fill some blank canvasses with lines and scribbles. And reflect on it, does it work well for sketching, or coloring.
Also observe others (watch tutorials, livestreams, process videos, or speed-paints) and try to mimic what people do that are good at digital art, it will help you understand how to do it yourself. You'll eventually get your own flow, maybe you'll make your own brushes and change the shortcuts and interface to optimize your workflow.
But for now I just recommend just seeing what SAI can do, and what you can do with SAI.