Learning scriptwriting and writing a screenplay is all about visual story telling.
It is a key ingredient that has much focus early in the movie project. It can and usually is rewritten a number of times before it makes it to the screen.
Scriptwriters are professionals who can take an idea and build a story around it. They must learn to captivate an audience through the visual representation of the material they write.
Anyone can learn to become a scriptwriter and develop skill with determination, practice and time.
You may adapt a play or book by writing a good script for it. A screenplay or script is not a novel however. It is not going to be read by the masses and become a best seller.
Screenwriters must attract film makers. Getting a script sold to a studio is a difficult task. The studios normally won't look at your work until they ask you for it and they don't normally ask unless they have either heard of you or your work.
Many scriptwriters enter contests which gets some visibility. Some try to get independent films made with their work with the intent to be submitted to film festivals.
If it gets noticed it could be picked up by a studio so there is much effort by writers towards film festival submissions.
Scriptwritng software is available but it won't help you create a winning script. You have to spend lots of time writing and rewriting the sript to develop the skills.
Personally I took a course with Chris Soth and found him to have a fantastic approach to screenwriting called the mini-movie method.
There are some good software packages you may consider like