Summary of the problem
The following image is a description of bootstrap icon.
I don't know how to use "Code point".
Unicode:
U+F120
CSS:
\F120
JS:
\uF120
HTML:

The following image is a description of bootstrap icon.
I don't know how to use "Code point".
Unicode: U+F120
CSS: \F120
JS: \uF120
HTML: 
For Using HTML code point, All you need is just set the the font-family of your element(or your body) to 'Bootstrap-icons' and then everything will work.
<!DOCTYPE html>
<html>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap-icons@1.9.1/font/bootstrap-icons.css">
<style>
.test
{
font-family:'Bootstrap-icons';
}
</style>
<body>
<div class="test">

</div>
</body>
</html>
I managed to find how to use CSS of "code point".
Add following html into the head element of document.
Set font-family
to be Bootstrap-icons
.
And you can use css code point \F120
to fill the value of content
property.
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap-icons@1.8.0/font/bootstrap-icons.css">
<style>
h3::before {
font-family:'Bootstrap-icons';
content:'\F120';
}
</style>
The otheres (Unicode, JS, HTML) are still ununderstood.
Thank you for reading my broken English! :)