In order to create a plugin, you need to CB SDK. You can start with this page: http://connectedbusiness.com/t-DeveloperResources.aspx
There is version of the SDK for each major version of CB. So get the SDK version that matches your version of CB. Not all of the SDK versions show up when you click the above link, so you need to further search for the correct version if you don't see your version on the list.
In order to build the development environment, you have to purchase DXperience, which is $1500.
Dynamic Enterprise Technologies Inc
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