How Do I Know Which Word to Use?

When i'm talking about similar words, i'm also referring to similar meaning. So for example, you learn this new word, and it's a little bit hard to say but you know, you can handle it. Then what if your teacher is like, ok, now, this word, which is totally new to you, also sounds like this other word? You wanta get a handle on one of these words before you move on to the similar ones. I strongly recommend everyone to avoid this.