Hi Dishen,
Are you trying to add new data programatically or through the interface?
If through the UI, you'll need to configure pages with the Create page association so you can launch the page in create mode.
If you are going to try do this programatically, you'll need to call the REST API for doing so. This will ensure the underlying tables will be populated correctly (for the parent entity, child entities etc). Entering data directly into the table in Postgres is not recommended. Calling the API will also ensure that data is indexed correctly as part of the insert.
Thanks,
Rory