Help developing a new plugin

I want to develop a plugin, I plan on making it 100% available for free.

But I am not 100% sure where to start.  On 4.0.

I see this: http://docs.nopcommerce.com/pages/viewpage.action?pageId=1442493

I want to create a plugin that customizes the contact us page to have a drop down to specify who to email.

Any direction you can point me in the code as an example?  I assume I need to create an override for the contactus view, some setting page to enter the data, and hijack the contactus submission.  Just not real sure were to start.

I have my site 80% stood up and ready to go live on NopCommerce, just ironing out the details like this.  I can just post a link to the email to start if I have to, but I've always preferred forms for emails.

Hi,

You can refer documentation and other plugin those are available in default nopCommerce 4.0 project.

And some forums question and answers

Thanks,
Jatin