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:
Box 1: Yes
Class extension - Method wrapping and Chain of Command.
The functionality for class extension, or class augmentation, has been improved. You can now wrap logic around methods that are defined in the base class that you're augmenting. You can extend the logic of public and protected methods without having to use event handlers. When you wrap a method, you can also access public and protected methods, and variables of the base class. In this way, you can start transactions and easily manage state variables that are associated with your class.
Box 2: Yes
In the following example, the wrapper around doSomething and the required use of the next keyword create a Chain of Command (CoC) for the method. CoC is a design pattern where a request is handled by a series of receivers. The pattern supports loose coupling of the sender and the receivers
[ExtensionOf(classStr(BusinessLogic1))]
final class BusinessLogic1_Extension
{
str doSomething(int arg)
{
// Part 1
var s = next doSomething(arg + 4);
// Part 2
return s;
}
}
Box 3: Yes
Instance and static methods can be wrapped by extension classes. If a static method is the target that will be wrapped, the method in the extension must be qualified by using the static keyword.
Box 4: No
Wrapper methods must always call next.
Note: Wrapper methods in an extension class must always call next, so that the next method in the chain and, finally, the original implementation are always called. This restriction helps guarantee that every method in the chain contributes to the result.
In the current implementation of this restriction, the call to next must be in the first-level statements in the method body.
Here are some important rules:
Calls to next can't be done conditionally inside an if statement.
Calls to next can't be done in while, do-while, or for loop statements.
A next statement can't be preceded by a return statement.
Because logical expressions are optimized, calls to next can't occur in logical expressions. At runtime, the execution of the complete expression isn't guaranteed.
Reference:
https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/extensibility/method-wrapping-coc

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:
http://axhelper.com/?p=16527