Verstaan is when you can hear what someone is saying: ik kan hem verstaan. (i can understand him/ i hear him) Begrijpen is when you understand what someone is saying: ik begrijp what je bedoelt. (i understand what you mean) So in the case of: ik versta je, maar ik begrijp niet wat je bedoelt. You can hear what he is saying, but you do not understand what he means by it.

Verstaan is when you can hear what someone is saying: ik kan hem verstaan. (i can understand him/ i hear him) Begrijpen is when you understand what someone is saying: ik begrijp what je bedoelt. (i understand what you mean) So in the case of: ik versta je, maar ik begrijp niet wat je bedoelt. You can hear what he is saying, but you do not understand what he means by it.