can you understand?和do you understand?还有are you understand?有

can you understand?强调对方是否“能够”理解,
而do you understand?强调对方是否理解这一结果。
没有太大的区别。
are you understand?(语法错误）
例：
Can you understand it now?
这一点现在你明白了吗?
I can hardly understand you。
我的几乎不懂你的话。
Do you understand French?
你懂法语吗?
Do you understand me?
你明白我所说的话吗?