The Pavilion theme package you download from Themeforest.net does not include OpenCart. You must have a working OpenCart installation before attempting to install Pavilion.
The installation steps for OpenCart 1 and OpenCart 2 are slightly different. Please, choose the documentation page that corresponds to your OpenCart version and follow the instructions there:
If you are new to opencart world, you could take advantage of the following tutorials and articles. They vary from installation steps to providing help for common opencart operations.
1. Official opencart documentation
2. Introduction to OpenCart video
3. Stackoverflow opencart section
4. Tuts+ starters guide for OpenCart
5. Several sites with various tutorials [link1] [link2] [link3] [link4] [link5]