In fact, I'm not sure the difference between guarantee, ensure and promise exactly. "保证" is used in several ways as follows: verb. 我保证(promise)会达到你的要求。 收到这个礼物，我保证(guarantee)你会满意。 我不能保证(ensure)他会准时抵达。 noun. 这条项链有附保证书。 跟银行借钱要有保证人才行。 Generally speaking, "保证" is widely used in “make sure”.

to guarantee; to ensure; to promise; to certify for; to vouch for; to give one's word all of them are right. .(to promise) is the most common use of 保证。 如：我们保证提前完成任务。 we promise to finish this task in advance.