Help getting $_POST data field names for entry

I’m new to EE and extensions.

I’m trying to write an extension to be added in a field underneath the Body field inside the Publish screen. I’ve had success getting the extension set up and running… though I’m having trouble with the final stage of the extension… which is inserting to the db. What I am unsure of is the specific calls of some of the $_POST data from the other fields from the Publish screen. Like the Title field, Date fields, body fields… how can I get access (correct syntax) to them in my process form file function.

For instance… if i wanted to access the Entry Date, would I get the string by:

$need_date = $_POST['entry_date'];

// or

$need_date = $_POST['field_list_items']['entry_date'];

// I'm unsure

Any help would be appreciated.

Thanks.