Transition from single celled to multi cellular

[TheDeafPianoTuner]

Hi, this is a topic I'm interested in knowing more about. I found a few things on a brief google/youtube search, the jist of it that I got was that single celled organisms began to band together, but I am still struggling to understand how that eventually got to what we have today with a multicellular organism, which starts off as a single cell, and as it divides the cells become more specialized (even that process I am still trying to grasp but I think I kinda get the idea).

If anyone has any links to articles / videos (preferably videos with pictures I like that!) I would be interested. Or if its something simple that I'm just not getting and you can explain to me I'd appreciate that too

Thanks!