it takes sb sometime to do sth

意思是花了某人多长时间去做某事。如：

It takes me 3 hours to prepare the dinner.

做饭花了我三个小时。

在这里，it是形式主语，指代后面的动词不定式，动词不定式才是真正的主语。

花某人多少时间去哪里

花了我一个小时去机场

It takes me an hour to go to the airport

花费某人时间去做某事
比如 it takes him sometime to do the homework.
做作业花了他很多时间

做某件事花了某人多少时间.
如:
It took me 3 hours to finish the homework.
我花了三个钟头才做完作业.
It won't take you long to read this notice.
看看这则告示不会花你多少时间.