To write your data access layer, you will need the early bound entities generated as per the Creating early bound entity classes recipe from Chapter 3, SDK Enterprise Capabilities; optionally, you can generate the enums for the status codes.
The status code enums are generated by default if you generate the class using the Developer Toolkit add-on for Visual Studio.
Additionally, you will require the solution created in Creating a Visual Studio Solution for Dynamics 365 customization.
To execute the code, you will require the appropriate privileges on the entities you are manipulating.