write something to someone
1. to send specific information to someone in writing. I wrote the facts to John, and he thanked me for the information. They wrote all the details to me, and I filed them.
2. to compose a letter or e-mail and send it to someone. Sam wrote a letter to his father. Did you write that memo to Mark yet?
write something to something
to write something that is supplementary to something else. Molly wrote an epilogue to her story covering the time up till now. I will write the introduction to the book this afternoon.
write to someone
to compose a letter or e-mail and send it to someone. I will write to her again, but I don't expect to hear anything. Please write to me as soon as you can.