I just bought/downloaded a template from Themeforest. How do I get started on Wordpress to do my website?
First of all you need to have a hosting for your website. Then you have to install wordpress on it. Finally you should follow the theme documentation instructions about how to install and set up the theme.
If you are not familiar with WordPress or web development in general, maybe you should start by learning about wordpress and basic stuffs about web development. You can found a lot of useful resources on Envato Tuts+: http://code.tutsplus.com/series/how-to-get-started-with-wordpress--cms-955
This has been dealt with downloading