使 is used in written Chinese， while 让 is in spoken Chinese more often... in your examples, both 让 and 使 mean "cause, bring out certain results" and 让 can be used as a verb. eg. 让他走吧。Let him go. Negative form: 别让他走。 Don't let him go. 他不让我走。He doesn't allow me leave. I don't suggest you try to relate certain English words with Chinese characters, it's fun though....try to think in Chinese, 别让 English interfere with it.

It's really difficult to explain. We are not languge experts. Generally speaking, they are almost the same. I believe that you can simply copy how we use it, which is the best solution.

它們的意義是一樣的。 如果一定要分，在我個人的用法中，“这使我很高兴”較為正式，“这让我很高兴”較偏向口語。 p.-s.還有另外一個字也是同樣的用法："这令我很高兴"。

就像英语中的let和make,哈哈，我就只能这么解释了

對個別的字 分別作字面上獨立的解釋 並不能讓你一窺全豹 建議自行搜尋關鍵字 " 兼語句 " 以便更進一步了解其使用法 (兼語句 pivotal sentence)