One possible version ：
I am glad to have received your letter. Now I can't wait to share with you what I did during the holiday.
For a month， I worked as a volunteer in a primary school in Guizhou， where I taught the students drawing. The students showed great interest in my lessons and a few of them did have a gift for art. We got on very well. At the same time, I learned to plant vegetables and gained much agricultural knowledge. Life was tough there. Compared with those children, we are really happy. So we should value our life and help those in need.
How was your summer holiday? Looking forward to your letter!