Nostr doesn't subscribe to any ideals of "free speech" as these belong to the realm of politics and assume a big powerful government that enforces a common ruleupon everybody else.
Nostr instead is much simpler, it simply says that servers are private property and establishes a generalized framework for people to connect to all these servers, creating a true free market in the process. In other words, Nostr is the public road that each market participant can use to build their own store or visit others and use their services.
(Of course a road is never truly public, in normal cases it's ran by the government, in this case it relies upon the previous existence of the internet with all its quirks and chaos plus a hand of government control, but none of that matters for this explanation).
More concretely speaking, Nostr is just a set of definitions of the formats of the data that can be passed between participants and their expected order, i.e. messages between clients (i.e. the program that runs on a user computer) and relays (i.e. the program that runs on a publicly accessible computer, a "server", generally with a domain-name associated) over a type of TCP connection (WebSocket) with cryptographic signatures. This is what is called a "protocol" in this context, and upon that simple base multiple kinds of sub-protocols can be added, like a protocol for "public-square style microblogging", "semi-closed group chat" or, I don't know, "recipe sharing and feedback".