in addition to what Ali said, it's better to know that متوجه شدن is more polite than فهمیدن. if you're talking to your supervisor, teacher or anyone whom you respect and when you want to say: "do you understand what I say?" it's considered to be rude to say: میفهمید من چی میگم؟, so it's polite to say: متوجه میشید من چی میگم؟