That depends a little bit on what you have as a code base.
In my page I have come Icons in the sidebar, so I add them here
which generates the bottom line in the left sidebar at https://ronnybergmann.net
But that also depends on how your Layout is defined and whether you have a sidebar. The navicons are then styled with CSS. And I am using font awesome icons (as well as academicons).
But maybe this helps as a starting point to check you _layout html files.