PBIReportHelper.initializeReportControl method is used to embed a Power BI report (.pbix resource) in a form group control.
Reference:
https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/analytics/add-analytics-tab-workspaces?
toc=%2Ffin-and-ops%2Ftoc.json

Explanation:
Box 1: Table extension
Isolate all new vendor exclusion codes as a new assembly by creating a table named VendExclusions.
Implement the Excel integration for the Vendor Exclusion List form.
The table extension object allows you to add additional fields or to change some properties on a table provided by the Dynamics 365 Business Central service. In this way, you can add data to the same table and treat it as a single table.
Box 2: Unique key
Create an index for the table named PrimaryIdx that uses the following fields: CustAccount, ItemId, VendAccount.
Box 3: Build and synchronize the database.
A project property lets you specify that the synchronize operation for the database should be performed every time that you build the project. This can be useful when you're making changes to the table structure for an application. Each time that you build, you will know that the database is synchronized with the tables as they are defined in the project.
Reference:
https://docs.microsoft.com/en-us/dynamics365/business-central/dev-itpro/developer/devenv-table-ext-object
https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/dev-tools/build-operations#synchronizing-the-database-at-each-build

Explanation

Scenario: CashDisc form
You must extend the CashDisc form to add a new field named MinimumInvoiceAmount to the form. You must add a new Extended Data Type to the extension model for the new field. The new field must be added above the discount method field. The field must display 10 characters.
Box 1: extension
To add a new field to an existing table, you must first create a table extension.
Box 2: field
Box 3: field group
Box 4: data source
Often, the information that is stored in existing tables doesn't satisfy customer requirements. Therefore, additional tables must be created, and data from those tables must be shown on pages.
You can add new data sources to existing forms through extension. Follow these steps.
* In the extension model, create a form extension for the selected form.
* Right-click the form extension, and then select New Data Source.
Reference:
https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/extensibility/add-datasource

Reference:
https://community.dynamics.com/ax/b/technicaltutorialsformsdynamicsax2012/posts/update-and-update-recordset-code-sample-in-ax-2012