All the courses and lesson plans you create will be available to re-use year after year. However, they won't automatically be assigned to your student unless you drag them over from the "Filing Cabinet" to your student's new "Learning Plan."
The "Learning Plan" for each student for each school year is where you start fresh. The only courses or lesson plans that are ACTIVE are the ones listed under your student's name. If you would like to unassign a lesson plan or course from your student's Learning Plan, just highlight the unwanted item and select "Unassign" from the little triangle drop-down menu in the top right corner of his or her column. DO NOT unassign anything from past years however or it will also remove all records of work completed.
You can make sure you are working with the correct school year by checking the top right corner of the "Learning Plans" page.
If you would like to hide unused courses and lesson plans, you can make categories called "Archive" or "3rd Grade" or "History" or whatever works for you. To do this, just click the name of one course (or lesson plan) and drag it on top of another name. The two will then be grouped in a category called "New Category." Just click on that text to rename it and then drag any other items into the category. You can also make subcategories inside of categories the same way.
I hope all of that makes sense . . .