A practical reference for Salesforce Marketing Cloud.

%%[
SET @email = AttributeValue("EmailAddress")
SET @name  = Lookup("Customers", "FirstName",
                    "Email", @email)
IF Empty(@name) THEN SET @name = "customer" ENDIF
]%%
Hello, %%=ProperCase(@name)=%%!

SELECT SubscriberKey, EmailAddress, CreatedDate
FROM (
  SELECT *,
    ROW_NUMBER() OVER (
      PARTITION BY EmailAddress
      ORDER BY CreatedDate DESC
    ) AS rn
  FROM Leads_Import
) AS t
WHERE t.rn = 1

<script runat="server">
Platform.Load("Core", "1.1.1");
try {
  var de = DataExtension.Init("Leads_Import");
  var rows = de.Rows.Retrieve({
    Property: "Status",
    SimpleOperator: "equals",
    Value: "new"
  });
  Write(Stringify(rows.length));
} catch (e) {
  Write(Stringify(e));
}
</script>