To use the html code that you have posted above, you will need to put it in a html iFrame on your page.
https://support.wix.com/en/article/using-iframes-to-display-visible-content-on-your-site
If you want to do it in javascript which Wix uses, then you can simply look at previous forum posts about this as there are many.
Just use the search function for random number or something similar.
You can find a few in the related posts box on this very forum post that can help you immediately.
https://www.wix.com/corvid/forum/community-discussion/random-number-generator
https://www.wix.com/corvid/forum/community-discussion/how-to-add-a-random-number-to-a-database
If you go to the first link above, there is a n example on this website.
https://webiya.wixsite.com/rnd-number-example