Triggers on MSSQL?

Question

SQL Server

Okay... Let's say we have a query UPDATE users SET n = n + 123123 WHERE id = 581;
How can I get 123123 and 581 from this request and use it in a trigger?
Can you give an example, sir?
Or just explain me this code line by line please, I think there is a solution to my question here:

USE SampleDb;

/* Таблица AuditBudget используется в качестве 
журнала логов действий в таблице Project */
GO
CREATE TABLE AuditBudget (
    ProjectNumber CHAR(4) NULL,
    UserName CHAR(16) NULL,
    Date DATETIME NULL,
    BudgetOld FLOAT NULL,
    BudgetNew FLOAT NULL
);

GO
CREATE TRIGGER trigger_ModifyBudget
    ON Project AFTER UPDATE
    AS IF UPDATE(budget)
BEGIN
    DECLARE @budgetOld FLOAT
    DECLARE @budgetNew FLOAT
    DECLARE @projectNumber CHAR(4)

    SELECT @budgetOld = (SELECT Budget FROM deleted)
    SELECT @budgetNew = (SELECT Budget FROM inserted)
    SELECT @projectNumber = (SELECT Number FROM deleted)

    INSERT INTO AuditBudget VALUES
        (@projectNumber, USER_NAME(), GETDATE(), @budgetOld, @budgetNew)
END

Answer 1

inserted - a pseudo-table of inserted values ​​instead of deleted ones deleted,
that is, in deleted there are values ​​that were, and in inserted - new ones
in the case when you didn’t shoot yourself in the foot and the primary key is present - you can really identify what exactly changed, from what and to what .

Answer 2

and note that the above code will only log one record, even if many records are affected by the DML query.