To draw on the computer, you can go to Station P and download a software called CLIP STUDIO PAINT, which is at the top of the home page. But this is a paid software, and some other devices are needed, such as graphics tablet. Beginners are not advised to touch these things from the beginning, and practice hand-drawn kung fu first.

If it is hand-painted, you can practice sketching first. You had some sketching skills when you were a child, so you should be able to get started quickly. Both scene sketch and character sketch can be practiced. You don't need to draw at first, you can make a good shape first, and the style can be biased towards the sun. For example, if you see a beautiful scene in an animation, you can stop copying.

Finally, this is a process that needs to accumulate over time. It is estimated that it is difficult to achieve anything in a short period of time (not a gifted one). It takes a long time to draw an illustration like that at station P.

I hope I can help you and adopt it.