Yeah, I don't think you should ever say, "I don't understand", it comes off as lazy, you're making the other person do all the work. Give them a little more to

Yeah, I don't think you should ever say, "I don't understand", it comes off as lazy, you're making the other person do all the work. Give them a little more to go on, tell them what you've understood so far and what you need clarification on.