1. 无用的；无价值的
    If something is useless, you cannot use it.

    e.g. He realised that their money was useless in this country...
           他意识到他们国家的货币在这个国家一文不值。
    e.g. Computers would be useless without software writers.
           没有编软件的人，计算机就会毫无价值。

2. 无益的；无效的；不能收到效果的
    If something is useless, it does not achieve anything helpful or good.

    e.g. She knew it was useless to protest.
           她知道抗议是没有意义的。
    e.g. ...a useless punishment which fails to stop drug trafficking.
           无法制止贩毒活动的无效惩罚

3. 差劲的；不行的
    If you say that someone or something is useless, you mean that they are no good at all.

    e.g. Their education system is useless...
           他们的教育体制真差劲。
    e.g. He was useless at any game with a ball.
           任何球类运动他都玩不好。

4. 无能的；无用的
    If someone feels useless, they feel bad because they are unable to help someone or achieve anything.

useless

    e.g. She sits at home all day, watching TV and feeling useless.
           她整天坐在家里，看着电视，觉得自己一无是处。