Good tutorials to start with?

[Eraser]

I read a bit through the document cocov linked to and while it touches the subject, it doesn't really go into detail of modifying what data the server sends to the client.

As is possibly known, I have the intention of giving a player an objective (a textual description of what the player has to do) and I want the client to display this objective on the screen. I thought of expanding either the playerState_t or entityState_t structs to include this data, but strange things happen when I do this. Is it possible to do something like this without modifying engine code?

[^misantropia^]

Yes, through config strings or by piggy-backing on the unused stats members. Everything else is no go: the engine expects those structs to have a fixed layout.