Hi Reza, before you do, I suggest that you go to this website English Level Test- http://www.englishjet.com/english_courses_files/test_level.asp On the left hand column choose the level you think you are and take the test. That way you will be sure of which level you are at.

Intermediate means that you can speak and understand the language well enough to have common conversations using a good-sized vocabulary. Therefore, you need to make sure that you know the main rules of grammar and that you know a lot of words and phrases. To do this, keep studying, practice with others learning the language or natives, or try to watch movies/listen to music/read short stories.