Ok, one more try.
You -> Designer, seller, developer, author, someone who made that product.
Themeforest -> sellers of your products.
Freemarket(freelance marketplace) -> same as themeforest, sellers of your product.
License -> How your product is protected by copyrights. you can license it by your own meanings, but must be compatible to CMS license of cms for which you make if theme is case. Also sellers protect products by their own license. Check their website for terms how they protect it.
Exclusive rights of product - this means that product will be sold only once to buyer.
Non-exclusive rights of product - this means that product will be sold unlimited times to multiple buyers.
Exclusive author - this means that YOU will sell products only on themeforest and no where else
Non-exclusive author - this means that YOU will sell products on themeforest and on freemarket, and/or on another website, but all website must grant you to sell products as non-exclusive author to be able to sell on multiple websites.
places like themeforest prefer to sell products as non-exclusive because they are not designers of that product so they can't guarantee that this product is not sold somewhere else before it's sold on themeforest.