can someone explain to me how funding for tv works?

do networks get money from advertisers and then use that to pay the content creators?
arent those creators working for studios so shouldnt the studios be giving them money?
how much are studios and networks getting if the average tv director is getting ~$100k?
my roommate said that it basically works that the networks give the shows a little bit of starting money and that they basically have to fund the rest, is that true? are shows more or less having to pay to be on tv? how is all of this being affected by streaming services?

i really dont understand how any of this works.