What is the difference between @BeforeSuite, @BeforeTest, @BeforeClass, and @BeforeMethod in TestNG?

@BeforeSuite       → runs ONCE at very start of entire suite
  @BeforeTest      → runs once per <test> block in testng.xml
    @BeforeClass   → runs once before first @Test method in each class
      @BeforeMethod  → runs before EACH @Test method
        @Test        ← actual test
      @AfterMethod   → runs after EACH @Test method
    @AfterClass    → runs once after all @Test methods in class
  @AfterTest       → runs once after all tests in <test> block
@AfterSuite        → runs ONCE at very end of suite

public class SuiteSetup {

    @BeforeSuite
    public void globalSetup() {
        // Runs ONCE: Start test database, initialize ExtentReports,
        // load global config, start mock server
        System.out.println("Suite started");
        ExtentReportManager.getInstance();
        TestDatabase.startTestDb();
    }

    @AfterSuite
    public void globalTeardown() {
        // Runs ONCE: Flush reports, stop test database, send email
        ExtentReportManager.getInstance().flush();
        TestDatabase.stopTestDb();
        EmailUtility.sendReport();
    }
}

public class LoginTest extends BaseTest {

    @BeforeClass
    public void loginSetup() {
        // Runs ONCE per class: Navigate to login page, set browser cookies
        driver.get(config.get("baseUrl") + "/login");
    }

    @AfterClass
    public void loginCleanup() {
        // Runs ONCE per class: Logout, clear session
        driver.findElement(By.id("logoutBtn")).click();
    }

    @BeforeMethod
    public void beforeEachTest(Method method) {
        // Runs before EVERY @Test: Take note of test name, create ExtentTest entry
        ExtentReportManager.setTest(
            ExtentReportManager.getInstance().createTest(method.getName())
        );
    }

    @AfterMethod
    public void afterEachTest(ITestResult result) {
        // Runs after EVERY @Test: Screenshot on fail, log status
        if (result.getStatus() == ITestResult.FAILURE) {
            captureScreenshot(result.getName());
            ExtentReportManager.getTest().fail(result.getThrowable());
        } else {
            ExtentReportManager.getTest().pass("Test passed");
        }
    }

    @Test
    public void validLogin() { ... }

    @Test
    public void invalidLogin() { ... }
}