This question is based on this thread.
Problem: to access MySQL\'s manual when the cursor is at the beginning of the word by
Ctrl-A
While I'm not sure how to start you off creating a wrapper for vim to do exactly what you want, I might make a suggestion on how you can achieve a similar effect with a function built into vim.
:! will allow you to run shell commands with a similar interface to vim's K command. It might not be the cleanest way to do it, but by using :! you should be able to call the MySQL manuals for a given term quickly without completely leaving vim.
If you really need to write your own plugin for vim, this article might be able to give you some pointers and a handhold on where to start.
I hope this helps!