Skype is a pretty sound tool to use when dealing with a VA you've outsourced somewhere abroad. With it's screen sharing features it's the best way to talk and show them what you need to be done. On that same note, you can also use any of the popular screen recording software, and have it saved for future reference should you have to train another VA.
I personally just voice record my directions or tasks, and email it. Then at the end of the day, for my email updates received, the task list is typed up with a checklist when it's completed.