Split a single row from column in into as many rows as words are in the string

If you want to to use STRING_SPLIT wit a column from anoter table, you need some more code for it

CREATE TABLE test_table(id int, name varchar(100))
GO

INSERT INTO test_table VALUEs (1,'Test text'), (3,'The UK declares war on Germany')
GO

SELECT a.*
FROM test_table  as t
    CROSS APPLY STRING_SPLIT(name, ' ') AS a
 WHERE t.id = 3;  
GO

| value    |
| :------- |
| The      |
| UK       |
| declares |
| war      |
| on       |
| Germany  |

db<>fiddle here