Learn English – what is the difference between ’em and them

They are different words with different meanings, except in colloquial language (slang), where they are often used interchangeably.

1) Usage of 'them': it's the accusative form of 'they' (3rd person plural) so use it in sentences where a 3rd party (someone/some people separate to 'they') is doing an action to 'they'.

Usage of 'these'/'those': they are demonstrative pronouns - the plurals of 'this' and 'that' - so use them to demonstrate something. 'These' is used for items that are in some way closer, more related, or in another way are the more important items of a sentence.

2) Examples of 'them': "John was asked what he thought of them."; "After I gave them a detention, I told them that they weren't making enough effort."

Examples of 'these'/'those': "Why are you trying those shoes on? These ones are much cheaper."; "Those people are silly, these are clever."

Hope this is clear enough and helps! If it does, an upvote and/or accept wouldn't go amiss!

There is no difference in meaning although there are a few differences in usages. Here, there is virtually no difference:

You are flying to Belgium tomorrow.
You're flying to Belgium tomorrow.

However, there are places where the two are not interchangeable. For example, this particular contraction cannot be used at the end of a sentence, or as a standalone sentence:

Who is flying to Belgium tomorrow?
CORRECT ANSWER: You are, Tim.
INCORRECT ANSWER: You're, Tim.

The same principles hold true for the other related contractions:

I'm ➝ I am
He's ➝ He is
They're ➝ They are
We're ➝ We are