First you will have to ACTIVATE THE DEV-MODE (DEVELOPER_MODE) in your Wix-Editor. Take a look on the given option-menu-panel on the top of your editor, you will find this option there.
After you have activated the DEV-MODE, you will be able to see and write CODE.
Navigate to the page you want to add your CODE.
Once opened your wanted page, you will find an already prepared little example-code, which can be found on every new created page of your site.
Something like …
$w.onReady(()=>{
...your code here....
...your code here....
...your code here....
...your code here....
});
Here you can start to create all your wanted features and functions by writing CODE.