understand syntax of store procedure

I'm new to store procedure, some of the syntax i dont know what is the purpose
SELECT CONVERT(NVARCHAR(10), [TrsDate], 103) AS [Date] ,[TrsDate] As [TransactionDate] ,CAST(YEAR([TrsDate]) AS VARCHAR(4)) AS [TrsYear] ,CASE WHEN MONTH([TrsDate])< 10 THEN '0' ELSE '' END + CAST(MONTH([TrsDate]) AS VARCHAR(2)) AS [TrsMonth] ,CASE WHEN DAY([TrsDate]) < 10 THEN '0' ELSE '' END + CAST(DAY([TrsDate]) AS VARCHAR(2)) AS [TrsDay] WHERE b.VoidStatus <> '1' AND b.TrsDate BETWEEN @p_DateFrom AND @p_DateTo AND b.SubTotal >= 0 AND b.VoidNote = 0 AND bd.VoidStatus <>'1' AND bd.Quantity >= 0 AND ReversedBill.ReversalBillNo IS NULL what it try to convert ? case, when, then, end is like the if else? must start from case, than case when? <>'1' what is this mean? not found when search on internet Thank for explain to me ~