ODK Build - conditional questioning, rearranging questions, saving forms

I have started using ODK build to write a data collection tool but have run
in to problems. Please can someone help with the following:

  1. How to write conditional questions. eg when future questions depend on
    the answer to previous ones. I have tried using branch but it is not clear
    how this works

  2. The website says it is possible to drag and drop questions but I have
    not found this. Am I doing something wrong?

  3. I cannot save forms. I go to file> save form as, and then it says it is
    saved with my file name, but when I go to open it, it says I have no forms

Many thanks