1. Go to the doctype you need to see corresponding table
In this example we will use Journal Entry, go to Menu->Customize
Below screen will display after you click the Customized button
Take note of the table name, every master data and transaction data table in the system has the prefix of "tab". The pattern of table name in the system is "tab"+DocType name = `tabJournal Entry`, that's how you get the table name.
Field name is straightforward.
2. To get the child table do the following
After you click the child table below screen will display.
Similar pattern follows with the rest of the table in the system
Hope this help finding the DocType corresponding table and field in the system.
Happy Learning!