Hi,
There are sample plugins in the SDK so start with those for the basic setup and framework.
When a plugin is executed in create-mode, all fields are submitted, even blank ones, but when the plugin is executed in update mode only the changed fields are submitted, so if you want to fetch certain fields using a plugin you might need to have a look
in the image too.
I'm sorry about the roughness of the answer but there are a lot of unknowns in you question to be able to answer, have a look at the examples in the SDK and return if there's something that's unclear.
Regards
Rickard Norström Developer CRM-Konsulterna
http://www.crmkonsulterna.se
Swedish Dynamics CRM Forum: http://www.crmforum.se
My Blog: http://rickardnorstrom.blogspot.se