A possible version:
Dear Li Hua,
Thanks for your letter. I am very glad to tell you about my life and study here as an exchange student in California, the USA. Six months ago , it was my first time that I had been to the USA, so it was really difficult for me to fit in with the life here. On my arrival here, I couldn’t understand what people said or communicate freely with them in English, and nor could I get used to the different study pattern here, so I missed home a lot. Fortunately, I have adjusted myself to the new surroundings as soon as possible and seized every opportunity to practice speaking English with the local people. As a result, now I have made rapid progress in oral English and felt at home to live here. What’s more, I’ve also attended the preparation course which helps me to get used to the academic requirements in America and become a more autonomous learner.
Hope to see you again soon.
Best wishes.
Love,
Wang Ping