Learn English – “You are” vs. “you’re” — what is the difference between them

There are a few things I would like you to take note of:

1. Read: Don't stop reading. Try reading aloud and attentively. Try to listen to your own reading. The more you read, the more your ears get accustomed to normal English constructs.

2. Write: The more you write, the easier it is for you to remember new words, grammar usage etc. Practice of writing would make your thought process fluent.

3. Learn and memorize new words: Increase your vocabulary. The more words you learn, the better you'll be able to express your thinking to a correct degree and in the correct way. Learn synonyms and antonyms. Synonyms will prevent you from feeling at a loss for words to express yourself. Antonyms can also help you remember a certain word in certain contexts.

4. Watch English: Yeah, no kidding! I have tried it on myself. It works the same way as reading helps you. Your ears are likely to remember common constructs in English. But please don't go for learning dialects at the start. They would confuse you.

5. Think in English: Most of the time, the basic problem with non-native speakers is, they first think something up in their mother tongue and then translate it into English, which on the one hand makes your thought process lengthy and on the other hand several errors may be added to your speech even before you realize it. So when speaking in English, stop thinking in your mother tongue and try to think in English and express yourself in English directly.

6. Practice: There is no short cut for it. The more you practise the more you will improve. If you have nobody around you, talk to yourself standing in front of a mirror. This would help you observe yourself during speech. I often imagine myself within a debate and talk as if I were having a conversation with several people at once. Believe me, it helped me a lot.

It's a contracted, or shortened, form of "them" that's used in conversation, much in the same way that "gonna" is often used to mean "going to". In your quote, there should be a space, so: "Let's kick 'em." The apostrophe is to show a contraction.

So yes, it's correct to use, and often used in conversation. However, if you are writing it, it should only be used to directly quote someone who has said it.