How do I add Median to this query?
You wanted inly explained how the syntax works.
But as complete Query


CREATE TABLE #TempListings
(
    ListingId int,
    Price money,
    UnitTypeId int,
    BedroomsAvailable int
)
INSERT INTO #TempListings VALUES(1, 1000, 1, 1)
INSERT INTO #TempListings VALUES(2, 2000, 1, 1)
INSERT INTO #TempListings VALUES(3, 3000, 1, 1)

INSERT INTO #TempListings VALUES(4, 1000, 1, 2)
INSERT INTO #TempListings VALUES(5, 2000, 1, 2)
INSERT INTO #TempListings VALUES(6, 3000, 1, 2)

INSERT INTO #TempListings VALUES(7, 1000, 2, 1)
INSERT INTO #TempListings VALUES(8, 2000, 2, 1)
INSERT INTO #TempListings VALUES(9, 3000, 2, 1)

INSERT INTO #TempListings VALUES(10, 1000, 2, 2)
INSERT INTO #TempListings VALUES(11, 2000, 2, 2)
INSERT INTO #TempListings VALUES(12, 3000, 2, 2)

INSERT INTO #TempListings VALUES(13, 5000, 2, 1)
INSERT INTO #TempListings VALUES(14, 6000, 2, 1)
INSERT INTO #TempListings VALUES(15, 7000, 2, 1)

INSERT INTO #TempListings VALUES(16, 8000, 2, 2)
INSERT INTO #TempListings VALUES(17, 9000, 2, 2)
INSERT INTO #TempListings VALUES(18, 10000, 2, 2)
GO




WITH #myselect
 AS (SELECT 
         BedroomsAvailable
         ,ListingId 
         ,UnitTypeId
         ,Price,PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY Price)  
         OVER (PARTITION BY UnitTypeId) AS MedianCont
    FROM #TempListings)
SELECT BedroomsAvailable 
    ,COUNT(listingid) AS Count 
    ,MIN(price) AS MinPrice 
    ,MAX(price) AS MaxPrice 
    ,AVG(price) AS AveragePrice
    ,STDEV(price) as StandardDeviation 
    , MIN(MedianCont) MedianCont
    ,UnitTypeId
FROM #myselect
GROUP BY BedroomsAvailable, UnitTypeId
ORDER BY UnitTypeId   
GO


BedroomsAvailable | Count |  MinPrice |   MaxPrice | AveragePrice | StandardDeviation | MedianCont | UnitTypeId
----------------: | ----: | --------: | ---------: | -----------: | ----------------: | ---------: | ---------:
                1 |     3 | 1000.0000 |  3000.0000 |    2000.0000 |              1000 |       2000 |          1
                2 |     3 | 1000.0000 |  3000.0000 |    2000.0000 |              1000 |       2000 |          1
                1 |     6 | 1000.0000 |  7000.0000 |    4000.0000 |  2366.43191323985 |       4000 |          2
                2 |     6 | 1000.0000 | 10000.0000 |    5500.0000 |  3937.00393700591 |       4000 |          2


db&lt;&gt;fiddle here