What did mark zuckerberg do to eduardo in the social network? Read details?

like how did he trick him? how did he have it so that his ownership percentage of the company went down? did him signing those first papers cause that when they first discussed the deal or what was it when they said were you aware you were signing your death certificate? like what does a death certificate have to do with any of this? how would that cause that to happen? just can someone explain to me please this whole situation and how mark scrwed him over?