How to get one entity values and create record in other entity

Hi All,

I am new to plugin in crm 2016.I am trying to create a plugin for case entity and invoice.I have custom field name casetype(data type is optionset) i want to get that values and if the case type is incident i can select case type when creating or later i can change case type in update too  then i want to get create a record  in invoice with case title and assign case id to caseid  (lookup field)    its a relation to  invoice.

Thank You