As a Chinese in Canada, I went through the very process myself. I remember during the first three months I understood and talked little, and it was not until about 3 or 4 years later that I was able to talk fluently in English. My suggestion to you is, don't be shy, keep on trying. People in countries like the US, Austrilia and Canada, who welcome a great number of immigants and internaitonal students every year, are used to talking to new comers, and if they think you're stupid not to be able to speak English fluently, that's because they never underwent the language-leanring process themselves.
Oh, and one more thing, if there's a word or two that you don't understand in a sentence, try guessing the approximate meaning of the sentence and the words before you ask others or look into a dictionary. You can't always know every word in a sentence, most of the time, understanding the approximate meaning is good enough.
Best wishes to your studies and language leanring.