1.give/lend sb a hand 帮助某人
We gave him a hand bringing it back.
我们帮他把它弄了回来。
He thanked all who had a hand in his release.
他向所有帮助自己获得释放的人表示感谢。
I'd be glad to lend a hand.
我很乐意帮忙。
I could see you'd want a hand with the children
我能看出你需要有人帮着照看孩子。
以上4例摘自《柯林斯高阶英汉双解学习词典》
Let me give you a hand with those bags .
我来帮你拎那些包吧。《牛津高阶英汉双解词典》
The neighbours are always willing to lend a hand .
邻居们总是乐于帮忙。
I went over to see if I could lend a hand.
我过去看我能不能帮上忙。
Do you need a hand with those invoices?
要不要我帮你处理那些发票？
2.give sb a big hand （或者give a big hand to sb）热烈地欢迎某人;
为……而(长时间持续不断的)热烈鼓掌，喝彩
不要想当然地以为是“帮某人一个大忙”哦。也千万不要理解为给某人一个大嘴巴或大耳光，如果别人和大家说give him a big hand你冲过去打了人家一巴掌那就尴尬之极啦！
Let's give a big hand to Sally for singing so beautifully tonight.
让我们为莎莉今晚美妙而出色的演唱热烈鼓掌。
Ladies and gentlemen, let's give a big hand to our special guests tonight.
女士们、先生们，让我们以热烈的掌声欢迎今晚的特邀嘉宾。
The team was given a big hand when it took its place on the field.
球队一出场，观众便给予他们长时间的热烈鼓掌。
Let's give' em a big hand.
让我们为他们热烈鼓掌。《柯林斯高阶英汉双解学习词典》
As soon as the film star appeared on the stage, the audience gave her a big hand.
那电影明星一上台，观众们就报以热烈的掌声。
Give yourselves a great big hand. You deserve it.
给你们自已一些热烈的掌声这是你们应得的！
Let's all give them a big hand for their marvellous creations.
让我们大家为他们的精彩杰作向他们鼓掌祝贺。
Let's give her a big hand!
让我们以热烈的掌声欢迎她吧！
Let's welcome our special guest and give him a big hand!
让我们用热烈的掌声欢迎特邀来宾！
Now, " said the compere, "this little girl has traveled all the way from Liverpool to sing to us tonight. So let's all give her a big hand."
节目主持人说："今天晚上，这个从利物浦远道而来的小姑娘将为我们演唱，让我们热烈鼓掌欢迎她。"
I got a big hand for dancing so well.
因为跳舞跳得很好，我得到了大家热烈的掌声。
另外“鼓掌”还有一个比较正式的表达是applause，上述表达中的big hand就可以替换成applause。
What a wonderful speech! Let's give her a round of applause.
好精彩的演讲啊！让我们给她热烈的掌声。
She got a round of applause when she finished.
她讲完时得到一阵掌声。
这里的a round of applause=a short period of applause
Clap one's hands 鼓掌；拍手
We all clapped our hands hard after the performance.
演出结束后，我们热烈地鼓掌。
那么问题来了“打他一巴掌（一耳光）”用英文该怎么说呢？很简单，就是“slap him in the face/give sb a box on the ears”。
box sb s ears/give sb a box on the ears 打某人耳光
slap him in the face又可引申为“泼冷水”和“当头棒喝”。
英英释义：A set phrase used to describe words or actions that have offended or otherwise upset someone.
It's a slap in the face for the 20 years of work we have done.
这是对我们二十余年工作的一记响亮的耳光。
I'm gonna be one of his helpers. It's just such a slap in the face, y'know?
我将会扮演他的一个助手，这简直是当头一棒，你们明白么？
His mother gave him a box on the ears.
他妈妈打了他一记耳光。
在网络用语中还有一词叫“打脸”，意思是指某人前后言行不一，导致自己处于一种很窘迫难堪的境地，那“打脸”英文该怎么说呢？我们可以用“have a egg on one's face”，大致意思是说某人表演很差被人扔鸡蛋，渐渐地就被用来表示“受窘；丢脸；难堪”。
They were left with egg on their faces when only ten people showed up.
只有十个人来了，他们感到很尴尬。
“slap in the face”也有这层窘迫的意思。
Life has given them a slap in the face.
生活给了他们一记响亮的耳光。
The Sun calls it a massive slap in the face for the United States government
《太阳报》称之为打在美国政府脸上的一记重重的耳光。
lose face ：to be less respected or look stupid because of something you have done
因为做过某事，不受到尊重，或者显得很愚蠢
England doesn't want a war but it doesn't want to lose face
英格兰不想打仗，但也不想丢面子。
Many leaders don't want to lose face by admitting failures.
许多领导不想因为承认失败而丢面子。
save face保住面子
She claimed they'd been in love, but I sensed she was only saying this to save face.
她宣称他们相恋了，但我感到她这么说只是想挽回面子。
He purposely made those remarks in order to save face.
他因爱面子而故意说那些话。
The scandal was hushed up in an effort to save face.
为了不丢人，没有把这一丑闻张扬出去。