As others have said this is known as a [`PIVOT`][1]. There are several ways in which you can transform your data from rows into columns of data. 

If you know the values ahead of time, then you can hard-code the values. Prior to the `PIVOT` function you would use an aggregate function with a `CASE` statement.

**Aggregate/CASE Version:**

    select sitecode,
      sum(case when [month] = 'Jan' then amount else 0 end) MonthJan,
      sum(case when [month] = 'Apr' then amount else 0 end) MonthApr
    from yourtable
    group by sitecode;

See [SQL Fiddle with Demo][2].

The `PIVOT` function was made available in SQL Server 2005, so if you are using that version or a newer one then you can apply that to your data.

**Static PIVOT:** 

    select *
    from
    (
      select sitecode,
        [month],
        amount
      from yourtable
    ) src
    pivot
    (
      sum(amount)
      for month in (Jan, Apr)
    ) piv;

See [SQL Fiddle with Demo][3]

The above two versions work great if you know the values ahead of time. If not, then you will use dynamic sql to create the result. 

**Dynamic PIVOT:**

    DECLARE @cols AS NVARCHAR(MAX),
        @query  AS NVARCHAR(MAX)
    
    select @cols = STUFF((SELECT distinct ',' + QUOTENAME(month) 
                        from yourtable
                FOR XML PATH(''), TYPE
                ).value('.', 'NVARCHAR(MAX)') 
            ,1,1,'')
    
    set @query = 'SELECT sitecode,' + @cols + ' from 
                 (
                    select sitecode, [month], amount
                    from yourtable
                ) x
                pivot 
                (
                    sum(amount)
                    for month in (' + @cols + ')
                ) p '
    
    execute(@query)

See [SQL Fiddle with Demo][4]

All 3 versions of this will return the same result:

    | SITECODE |  JAN |  APR |
    --------------------------
    |       XX | 4000 | 4000 |


  [1]: http://msdn.microsoft.com/en-us/library/ms177410%28v=sql.105%29.aspx
  [2]: http://sqlfiddle.com/#!3/73b2f/4
  [3]: http://sqlfiddle.com/#!3/07d60/2
  [4]: http://sqlfiddle.com/#!3/07d60/1