connect user to k2 group

What do you mean by (review) our existing fieldtype plugins? How can I try review the GJ Auto Integration and at the very top of it is the Field usage. Where can review our fieldtypes such as the File and Video fieldtype plugins
Thanks

You'll need to download the File and Video fieldtype plugins then edit their PHP files and XML files to review their source to help you create your own fieldtype plugin. There is also the Gravatar, Progress field, and a number of other fieldtype plugins we provide that you can review if needed.

I have downloaded video and Gavatar plugins PHP files and XML files but cant find File fieldtype? What part of the PHP and XML files should I review to help me create my own K2 fieldtype plugin? I am an amateur.
and How can I try review the GJ Auto Integration and at the very top of it is the Field usage?
Thanks

I have downloaded video and Gavatar plugins PHP files and XML files but cant find File fieldtype?

The file fieldtype plugin is an Advanced plugin so you can download it from the Advanced downloads section.

What part of the PHP and XML files should I review to help me create my own K2 fieldtype plugin?

All parts. You need to extract the zip and review the code of the plugin. Once you understand how it works you can begin creating your own fieldtype plugin. You can also download our API documentation in the free downloads section for further information on API usage and file locations. The below site also has a good bit of tutorials to help you with PHP, HTML, CSS, XML, and more usage.

www.w3schools.com/

I am an amateur.

Then you're going to have an extremely harm time implementing this. You may want to consider hiring a contract developer at sites like Joomlancers to develop this for you.

and How can I try review the GJ Auto Integration and at the very top of it is the Field usage?

Extract the GJ auto integration zip file and in the PHP file the field usage is at the very top.

I was looking at the new tutorial www.joomlapolis.com/support/tutorials/107-use-cases/18377-configuring-a-country-field-with-cb-query-field-pluginis so it possible to configure a query that can select a dropdown field for country then a dropdown for the state and lets say a post code dropdown then a k2 category drop down to select to join that category?
What would be the querys?
Thanks

Or could I use it to dynamically join a virtumart ACL user group on sign up as well as a k2 user group?
Thanks

Do I have to join GeoNames I couldn't work out how to achieve the demo above
Thanks

All it does is pull its values from a database query. It doesn't do anything more than that. So for a select field instead of having to add values 1 by 1 through CB > Field Management while editing a select field you could use a Query Select field and it'll pull its values from whatever database query you supply as shown in the tutorial.