Assure a person of something is to make him or her confident of it.
Assure是向他人承诺保证的意思，目的是让他人对某事某物建立信心。
Example:
I assure you that we will finally achieve the goal on time.
我向你保证，我们最终肯定能按时完成目标。
The company CEO said he assures all employee that the company will not cut off anyone in this unprecedented tough time.
在这个史无前例的艰难时期，公司CEO向全员保证公司不会裁掉任何员工。
Ensure something is to make sure it is going to happen.
Ensure是通过采取可行的措施确保某事某物发生的意思。
Example:
I need to study harder to ensure I can get passed on that vital examination.
我需要更加努力的学习从而保证我能顺利通过那个至关重要的考试。
He got enough scores from the game today, which ensures his team will have a competitive place in the final matches.
他今天拿到了足够的分数，这将确保他的团队在最终的比赛中占有一个有竞争力的条件。
Insure something or someone is to cover it with an Insurance policy. A agreement that ensure people can get compensation if something happens to someone.
Insure是保险担保的意思。 理解这个单词，可以从对应的名词形式insurance来理解。 Insurance就是很多人熟知的各种保险，比如重疾险。
Example:
I really don't want to insure my car, but i have to do it because the law asks.
我一点也不想给我的车上保险，但依据法律要求却不得不买。
The insurance company refused her insurance with an explanation of nature unpredictable disaster.
保险公司拒绝了她的保险赔偿请求，给出的理由是不可预知的自然灾害导致。
