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؟

These two words have similar meanings in many cases. In this example my answer is yes.look at these sentences: .من زبان ترکی را خوب متوجه می‌شوم - .من زبان ترکی را خوب می‌فهمم - both of above sentences are correct. but sometime فهمیدن used for show a higher level of understanding than متوجه شدن.

In addition to those description that were reliable too, فهمیدن is used in different cases more than متوجه شذن. مثال: حل مسائل ریاضی، مطالب درکی یا غیر انتزاعی و ضمنا نوعی درک کلی است اما متوجه شدن بیشتر حالت ناگهانی دارد. مثال: او متوجه نگاه بد شما شد. یا توجه کنید را نمی شود گفت:بفهید