The most basic difference is this:
If you sign up as EXCLUSIVE to Envato, you agree to not post any of those tracks to other sites. With this you will make a greater percentage profit from each sale - starting at 50%.
If you sign up as NON_EXCLUSIVE, you are allowed to post those tracks to other sites. However, under this agreement you will make less percentage profit from each sale - starting at 35%.
You are allowed to have 2 unique accounts if you wish. That is set up an Exclusive account and a Non-exclusive account - each with different tracks.
You should read THIS as a start to understanding Exclusivity. Check out all the other author related info linked from your Dashboard as well.