Have you searched this site for the information your requesting?
The OSI model is available here, along with the FTP protocol.
I'd recommend you read the following topics in the indicated order to help you understand and solve your question:
1) The OSI Model + Encapsulation/Decapsulation page
2) Protocols (Introduction)
3) TCP and UDP
4) Ftp Protocol
The data and instructions contained within a packet of a FTP session is not that much of interest when your trying to understand how the protocol works and transfers data from one point to another.
If you can understand the OSI reference model and how it users the underlying transport protocols (TCP and UDP) to service the above layer protocol like FTP or TFTP, then you can see the big picture and realise how it all works.
The instructions the ftp client and server send to each other is of little importance to us, since we are interested on how the transfering model works, and for this reason, it is important to understand the above suggested topics.
I would reccomend you download a protocol map.. basically what they show are all protocols at each layer of the OSI model, and how they interconnect.. I have one as a pdf but its too big to upload anywhere.. besides you can get them online..