How to put Share buttons on the bottom of my posts

I wasn’t the one that made the share buttons that were in the ghost site I’m working with right now.
Out of suddenly, the share buttons disappeared.
I’ve been for hours struggling to know and learn how to make them, but I just can’t.
Could someone please tell me how, in the simplest way as possible?
I need to put social share buttons in the end of all my posts (not the homepage)
What code should I put in code injection? what file should I create?