I cannot help you write this email, because it is important that you get the required guideline which would help you write better emails in future.
When writing an email to your friend, there are some things to consider such as:
Your language. As you are writing to your friend, your language and grammar will be informal and even colloquial as you are speaking to him as a familiar person.
The purpose of your email: You should go straight to what you want to tell him or her after exchanging pleasantries and jokes (as the case may be), and in this case, you're telling him about the interesting class you had.
The details: Be sure to include the details of the interesting class. Information like, who did what, to whom, here, when, should be included so that your friend will be able to understand how interesting the class actually was.
Conclusion: This is where you bid farewell to your friend, and promise to keep in touch.
Một ngày là khoảng thời gian Trái đất hoàn thành một vòng quay quanh trục của nó, mất khoảng 24 giờ. Một ngày Mặt trời là khoảng thời gian trôi qua giữa lúc Mặt trời đạt đến điểm cao nhất trên bầu trời hai lần liên tiếp.
