Querying and Creating New GRNs

I'm working on an application that takes in a structured .csv file and can't find any information on how to query and create new Goods Received Notes. I know that parts of them are stored in the titrec and tjourent tables, but adding to them manually causes Sage to complain, so I feel like I'm missing something. Using the SDK, I am successfully adding vendors and POs. Any help would be appreciated on how to use the SDK to add GRNs.