Installation issues. PLEASE HELP

This is probably such a stupid question but I am new to and I am trying to get the Intro theme because it has all the aspects I want in a theme for my blog. I CANNOT figure out how to get it installed. I went to documentation and followed the steps in the first video but I am lost after that. It is probably super easy but I am coming from Blogger and blogger was 10x more user friendly so I am just thrown off guard.

My website is

Thank you thank you thank you

Have a look at the official Codex page please.