Adding an element to my homepage

Hello, i have the following question: Im using the latest WordPress version with ‘Mystique’ Theme installed, and i’d like to add an element to my main page. Actually on my index there is one static page where almost all the content is, this is how i’ve set it up.

So i wanna add a ‘floating sidebar’ that would display on my front page. I already found the script on https://www.flooble.com/scripts/sidebar.php (meybe later on i’ll use something more advanced but for now i think it’s enough). Now i just dont know how to add it ?? Tried directly on my page-editing panel (HTML tab) and it doesn’t show up. Actually it does show up in the editing window as a static element, but then when i update it doesnt display on the home page.

I don’t know where should i insert it, i remember having this problem previously with something else i didn’t know how to solve this. Should i perhaps edit manually index.html? Im not sure if hmm the script doesn’t override it somehow. I don’t know just my guess because im newbie at this.

So what should i do, thank you.