How to make a part of your website embeddable and how to embed it?

Question

Like in a message or to paste the part into another site

Answer 1

You could use the iframe tag. E.g. like this:
<iframe src="your-url"></iframe>
This requires however a certain configuration of the web server and embeds a full website.
If you only need a part of the website I'd create a code snippet that can be reused every time you're working on other projects.