How to implement the exchange of goods with the Vk API?

Question

API

Good day!
Tell me how to implement the exchange of data (goods) with Vk.com ???
Those. the logic as I understand it is as follows:
- authorization of the user and obtaining the key
- request to the group and the formation of a list of goods
- comparison with the database
- request to the group to update and create goods
Of course, I count on good Samaritans, but I am ready to reward the great guru for help)))