To assure someone is to remove someone's doubts. To ensure something is to make sure it happens—to guarantee it. To insure something or someone is to cover it with an insurance policy.
Is ensure and assure the same?
Despite sounding alike, the words are not interchangeable. "To assure" means to promise or say with confidence. "To ensure" means to make certain.
How do you use the word ensure?
If you're trying to say make sure, then ensure is the correct word to use. Use ensure in the following ways: The dog owner always would ensure that he returned home quickly. Billy was to ensure that the computer was packed safely.