To log back into your lessons you can always click the 'Log into my studies' link at the top right of all pages.  Once there, simply click the 'Student Login' link at the top.  Once logged in, you'll see a 'Completed Lessons' link that will display the lessons you've finished along with a link 'Take Next Lesson' which obviously takes you to your next lesson.  That's about it!  Enjoy! 
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