Update stddevPop function documentation

docs/en/sql-reference/aggregate-functions/reference/stddevpop.md

@@ -13,4 +13,45 @@ Alias:
 
 :::note
 This function uses a numerically unstable algorithm. If you need [numerical stability](https://en.wikipedia.org/wiki/Numerical_stability) in calculations, use the `stddevPopStable` function. It works slower but provides a lower computational error.
-:::
+:::
+
+**Syntax**
+
+```sql
+stddevPop(x)
+```
+
+**Parameters**
+
+- `x`: Population of values to find the standard deviation of. [(U)Int*](../../data-types/int-uint.md), [Float*](../../data-types/float.md), [Decimal*](../../data-types/decimal.md).
+
+**Returned value**
+
+Standard deviation of `x`. [Float64](../../data-types/float.md).
+
+**Example**
+
+Query:
+
+```sql
+DROP TABLE IF EXISTS test_data;
+CREATE TABLE test_data
+(
+    population UInt8,
+)
+ENGINE = Log;
+
+INSERT INTO test_data VALUES (3),(3),(3),(4),(4),(5),(5),(7),(11),(15);
+
+SELECT
+    stddevPop(population) AS stddev
+FROM test_data;
+```
+
+Result:
+
+```response
+┌────────────stddev─┐
+│ 3.794733192202055 │
+└───────────────────┘
+```

docs/en/sql-reference/aggregate-functions/reference/varpop.md

@@ -31,6 +31,8 @@ This function uses a numerically unstable algorithm. If you need numerical stabi
 
 **Example**
 
+Query:
+
 ```sql
 DROP TABLE IF EXISTS test_data;
 CREATE TABLE test_data
@@ -47,6 +49,8 @@ SELECT
 FROM test_data;
 ```
 
+Result:
+
 ```response
 3
 ```
@@ -94,6 +98,8 @@ SELECT
 FROM test_data;
 ```
 
+Result:
+
 ```response
 0.5999999999999999
 ```