Dieter,
There are many plugins written for K2, take a look at the Joomla Extension Directory and there is nothing deceitful or dishonest about this at all.

I do not call myself a coder, more a styler, but managed to create my own pligin, K2MultiAds (also on JED).
You do need to have an understanding of Joomla code, compare the K2 plugin code.

To write a complete guide on writing a K2 plugin would no doubt be useful but plugin creation is typically done by devs with relevant experience.
As I am not sure where your skills lie, it might be worth explaining a little about what you would like to do.
If you send me a PM, I will send you a working, example of a K2 plugin.

Simon
K2 Support