Warning! This is only for people who want to be experts in Facebook:
This explains how a like vs a share vs a comment will impact a piece of content (e.g. post, picture, etc.) on Facebook.
What happens when you like content?
Liking helps a piece of content reach more of a person's, brand's or business's existing audience (their fans, friends or followers). If, for example, John's Pizza has 100 fans, only 5-10 of those fans see his posts regularly, because they are the ones who most click on his profile page to see what is going on. If all 5-10 of those fans like a particular post, Facebook presumes it's important, so they show it to 25 of John's fans who are the next most frequent visitors of his page, and so on. This is why you see engagement, marriage, baby birth or new job announcements from friends you are not that close with...and you'll notice those announcements already have many likes and comments on them. It's because Facebook recognized that enough people found those pieces of information more important than just a regular update and so more people in that person's network should see them.
What happens when you share content?
Sharing content exposes the content to the sharer's network. Let's say Tracy is one of the 5-10 who visit's John's Pizza's page frequently. She sees a new special he posts and she shares it. Of Tracy's 100 friends, the 5-10 who visit her profile page most frequently will see what Tracy shared (which is the post from John's pizza). If those 5-10 people all like it, it will be shown to more of Tracy's fanbase (as per the above). When someone shares content, it gets exposed to their network - if someone in their network enjoys the post and clicks through to the content creator (e.g. John's pizza), then the creator (John) enjoys an entirely new audience thanks to the sharer (Tracy).
What happens when you comment on content?
Comments are an interesting hybrid. A comment signals to Facebook that the content is interesting, so they will show it to more people in the content creator's network. Let's say Stephanie comments on John's Pizza's post (e.g. "Yum! Looks delicious!") - more of John's fans will see this piece of content because it got good engagement (in general, comments require more effort than likes, so they are weighted more heavily). Comments also tell Facebook that the commentor found this content interesting, which prompts them to show the content the commentor's network. Because Stephanie commented, Facebook will tell Stephanie's friends that she commented on this content, assuming that they, too, will find it interesting.
What the heck does this mean for me?
OK, OK. It can mean whatever you want. Most people ask us, "How do I get my content to become viral?" The truth is, you can't control virality, but you can give it a head start. Here's how:
1. Comment on it...something that shows pride and enjoyment - convey that the content is interesting to you so others will think it's interesting to them (comments are attached to content and get carried throughout networks so other people you don't know, who will see this content, can see your comment).
2. Share it...and tell other people to share it, too - this will bring the content to your network and, hopefully, people in your network will share it to their network with the same message and so on.