Richard‘s comments are excellent. I find myself using English idioms constantly and not even thinking about it. It’s not to be confused with slang. I don’t use slang at all, or very little of it. Slang would be like calling a car your „ride“ or „wheels.“ An idiom would be like, „I‘ll bet you a nickel that that’s what happened“ instead of „I think that’s what happened.“ The former is idiomatic because I’m obviously not betting anyone anything. I just said that to my 90-year mom the other day and she laughed and said I must be the only one saying that, since a nickel isn’t worth what it was in the 1930s. I said, „I probably got that from you mom.“

So, I do think you really need idioms as they are so commonly used and they do add a sense of fluency to your speech. But, like Richard said, if you’re not at near native fluency be careful you know what they mean, and how they are appropriately used. Otherwise you’ll risk embarrassing yourself. 

Ramy... I tell my students the following:

- Yes, you can learn the meanings of English idioms so you might understand them when you read or hear them, BUT

- Do not use them because they are figurative language, not literal language, and using figurative language is a skill that only advanced, near-native fluent speakers can use correctly, at the right time, and in the right situations. Mis-using an idiom could be embarrassing and could also offend the listener.

Others may have different opinions than mine.