Hi Juliana - to implement this, you would use an Inbound Interface with a "Custom Processor".
The help topic here https://docs.onenetwork.com/devnet/latest/platform-user-s-guide/integration/inbound-interfaces/custom has some basic information.
This doesn't go into much detail about how to write it to the database. Here, you would take the data out of the JSON, put it into Model objects, and use ModelDataService to write it. Remember that it is more efficient to execute 1 model write action with a list of 100 objects, than 100 model write actions with 1 object each.
Last point - if your JSON will be extremely large (multi-MB), this may require additional care and discussion. If it is not multi-MB in size, then the approach from the help topic should be fine.