(1)use sth as 用作为；把…当作…使用

You can use it as a bookmark.
你可以用它作书签。

The public has been asked not to use the places as rubbish dumps.
已向公众提出要求,不要把这些地方当作垃圾堆。

We use oil now as a fuel.
我们现在把石油当作燃料。

He used his job as a screen for his spying activities.
他利用他的工作掩护进行间谍活动。

(2)be used as被用作

This pole can be used as a fishing pole.
这杆可被用做钓鱼杆。

The space underneath could be used as a storage area.  

底下的空间可用作储藏区。

The mixture can be used as a gargle several times a day.  

每天可用这种混合液漱几次口。

Stone began to be used as a roofing material.  

石料开始被用作盖屋顶的材料。

At a pinch it can be used as a weapon.  

必要时可以把它当作武器.

The electric drill can also be used as a screwdriver.  

这把电钻也可用作螺丝刀.

Newspaper may be used as a vehicle for publicity.  

报纸可用作宣传工具.

Bark may be used as raw material for paper - making.  

树皮可以做造纸的原料.