了解 is something like you "know" something 理解 is you understand something

理解： 1.懂得事物的规律(understand the law or rule of one thing) 2.能站在某人的角度考虑到他所处的情景(stand on one's position and think about the thing) 了解： 1.掌握了某事件的进展程度(know the progress of a thing) 2.回顾某事件的发生过程(when an event happened, one person take action to know how to happen) 3.熟悉某人的性格(be familiar to somebody and know his or her personality and habits etc.) I firstly answer to a question in English and I am on the stage of learning English also. If I didn't express clearly, we can exchange opinions.

Dear pixiedust This is William from China To make it simple. 了解=know 理解=understand

First you 了解 something or someone and then after more and more times you can really 理解 someting or someone.

Thank you :)