Why do we use header and footer tags?

Answer 1

They are basically used by semantics. In any case, maybe this can help you:

https://www.w3schools.com/tags/tag_header.asp
https://www.w3schools.com/tags/tag_footer.asp

Answer 2

For proper content management and SEO purposes.
Here an example of using these html5 semantic tags.

https://code.sololearn.com/W87tMtRyJ1j5/?ref=app