How to remove a website from Safari?

If you mean removing a website from your Safari history, open Safari > Sidebar > History, find the site, then touch and hold it and choose Delete.

If you mean a bookmark, Favorite, or something showing on the Start Page, the steps are different. Which one are you trying to remove?

In addition to the guidance from our friend, @PreCognition, I submit for your reading pleasure: Safari User Guide for Mac - Apple Support