The root directory where your website's files are located. By default, the root folder of your website is public_html.
To open the root category using SSH, follow these steps:
Once there, run this command:
cd /home/u123456789/domains/domain.tld/public_html
Replacing /home/u123456789/domains/domain.tld/public_html with the value of the root folder path which you copied from hPanel.
That's it, you can start working with your website files.
Additional resources: