That’s a really good question. I think when you are a beginner, you most likely will have to use the dictionary. However, when you have got your basics down, you can switch to a thesaurus or an English dictionary without any explanations in your mother tongue. I think my other advice would be to learn through listening to online videos and movies. You will also learn a lot from conversations with native speakers (or someone who is proficient). They will be able to explain the meaning of words in simpler words that you already know. Depending what time of a learner you are, you might want to also write things down. I started learning English when I was 15.5 and went to study linguistics when I was 16 and graduated with a bachelors degree in 2010. There is nothing impossible! You just have to start somewhere and carefully pick the content of your lessons. Don’t try to jump ahead of yourself :)

Dictionaries are meant to provide definitions of all of the words in the English language. But to be a good English speaker requires a lot of practice. If you'd like to practice speaking, I'd be happy to help you develop a study plan. Feel free to look at my teaching profile and class offerings, and message me if you think I can help you.

I think your teachers want you to stop looking in the dictionary written in your own language because they want you to start thinking like a native English speaker. Often, dictionaries are written in your grammar and the way you phrase concepts in your own language. This may be a hinderance to learning how to speak and think like a native English speaker.