how can i create new entity's

how can i create new entity's, do i need to edit the game?

i want to make a new function and stuff.
do i need quakec?
can someone give me a good website on how to start with quakec?
also, I love this site.

Errmmm... Go looky the tutorials/articles pages on this site. I'm sure it still has a section to getting started with QuakeC and pretty much everything Quake modding related. :/