An overview of how to get started from scratch with Vim script
Vim comes with great documentation built in already. The interface to the
documentation is the :help command.
For an introduction, see :h user-manual.
Almost all Vim installations also come with an interactive tutorial:
$ vimtutor
Vim is decades old and still popular. You will find a lot of resources about it on the web, some better than others. The good ones are listed here.