I used to write. It means that, in the past, you wrote many times. But you don't write any more now. I'm used to writing. It means that you are accustomed to writing. It is natural for you. You write many times now.

Thank you!

What is your question?

I used to write = when I was a child, but now I don,t write ..for example .. I used to write my homeworks when I was a pupil. Now I,m not the pupil anymore.