Creating themes for themeforest

I am currently developing a theme for themeforest and it is almost over. I have some questions before launching it to themeforest.

1. How to license my theme.
2. How to add an installable option to my theme (not just copying files to directory).
3. How to add an option to activate theme with a license key.

I need to know all these stuffs are done by themeforest or it should be done by developer. I am not an experienced developer and if anyone can provide some details and how to do these i very much appreciate that.