assure就是让你去确认已完成或肯定会完成,可翻译为"保证".assure sb of sth/assure sb that ...

ensure就是让你付出努力,确保完成某事,可翻译为"确保".ensure sth/ ensure that ...

例如：1.You have to ensure that it is true.= you have to make sure that it is true.

2.I assure that it is true= I am sure that it is true.

assure的意思是：向……保证,使确信,让……放心,常用的结构是：assure sb that或者assure sb of sth,使某人相信某事.后面往往加sb.

ensure虽然也解释为“确保”、“保证”,但ensure后面往往不跟sb,而加sth,解释为“确保某事”