Derek and Jared update.

大家好！( 你们好吗？) (we usually use one of them, not both of them.)

我叫Derek （德里克） 。他叫Jared （杰里德）（after saying Hi, we introduce ourselves) 

我们学习中文已经三个星期了。(We have been studying Chinese for three weeks) 
"了"has the same use of " have been doing" such as 我吃饭了。 of course " 了" has a lot  of meaning. It depends.

我在Apple工作。他是老师。“在 do”means doing something right now.  such as 我在唱歌。I am singing。

再见！it is right in the grammar, but we don't say 再见 in the end of a letter. 再见 means goodbye or see you later in english. we usually say some good words to wish somebody lucky or show your best wishes. such as 祝：身体健康。 祝：家庭幸福。祝：天天开心。。。。。etc。

 have a good time here.

Derek and Jared update.

大家好！ 你们好吗？

我们学习中文已经三个星期了。(We have been studying Chinese for three weeks) 

我叫Derek （德里克） 。他叫Jared （杰里德）。

我在Apple公司工作；他是老师。 

再见！

Derek and Jared update.

大家好！ 你们好吗？

我们学中文已经三个星期了。(We have been studying Chinese for three weeks)

我叫Derek （德里克） 。他叫Jared （杰里德）。

我在Apple工作；他是老师。

再见！