Before I come to the US, I never studied Idioms or phrasal verbs. It didn't feel right to me in Egypt because nobody around me cared about Idioms. I used textbook English all my life in Egypt. Once I arrived to the US I studied hard phrasal verbs and idioms because everybody use it. At work, in college, in clubs, in gyms .... Idioms, expressions, phrasal verbs are used here in the states all time everywhere.

I don't keep track of it, but I think we use a lot less idioms in English as we would, in, say, Chinese. And yes, you would be able to express yourself without using any idioms. Sometimes, you may be using an idiom without realising it! Just take it as part of the language when it is common. When it is less common, use it for exams :)

Without idioms, you would sound like a talking computer. It's neither possible nor desirable. You don't have to study them though. Just try to understand whenever you hear another person use one. In that way you can pick them up one by one. rps.sky, note that there is no plural of "slang"; you cannot say "slangs".

It is perfectly Ok not to use any idioms, those are not mandatory part of speech. Idioms or slangs are often used when you are having very informal conversations with friends and relatives or any people you are well acquainted with. But for a non-native speaker it can be a double edged sword (and here you got one ;)) because if you do not know in what context to use it, that can lead to awkward situations. Personally I like to use idioms and slangs in an informal context because I feel like it has some sort of "smoothing" effect over the conversation, but that is just my way of seeing things of course.

Your questions are a simples questions,but interestings. Answer your firts question I need use idioms because i´m forced by my English teacher jajajaj. I use easy idiom to remember like ¨easy peasy¨ or drop me a line. Answer your second question,I think tha i will able to talk without idioms,but your vocabulary is a poor vocabulary.