If you use word stress in your speech, you will instantly and automatically improve your pronunciation and your comprehension. If you have an English teacher, you can ask her to help you understand word stress. Or you can try to hear the stress in individual words each time you listen to English - on the radio, or in films for example. Your first step is to HEAR and recognise it. After that, you can USE it.
Sentence stress is another golden key for speaking and understanding English.
We make the important words BIG and the unimportant words small. Now that you know that word stress exists, you can try to learn more about it.