Here are the slides:

e2ee-presentation.odp e2ee-presentation.pdf

Usually, this is how you interact with someone: each time you make a request to the internet (a Google search, sending a mail, sending a Signal message, going to Facebook, everything), you do not talk directly to the person you want to talk to (in case you want to share something with someone). There is always a middle man, called a server:

Every information that passes through the server can be seen by the server, which is administrated by some entity, which will at least cooperate with the police or other government agencies if needed.

This is something that can be prevented by using End to End encrypted services. With such services, you encrypt your message on your own laptop, then send it to the server that will only pass it to someone, who will decrypt it on their own computer: the server only has access to encrypted data.