To give a brief over view, back in 2012 FB ran a lab-rat experiment on users to keep them in an "echochamber" (without notifying the users) doing so while reducing the posts that you see.
So if you're a conservative, you only see conservative posts..etc. So that you're stuck in a feeback loop and don't see different opinions, so that people become more extreme and more divided.
Later on, in 2014 some company took advantage of Facebook's new "brain manipulation" algorithm and took advantage of those feedback loops to keep infuse "fake news" to a targeted audience.
That's basically a short overview, but there's a lot of stuff in between.
Hope that helps :)
Yes, nice of you. :-) Thank You !