How does television do it?

I just started watching two television shows called Orphan Black and Sleepy Hollow. I am into the sci-fi/fantasy/drama genres..

In my opinion these episodes are well written and each episode ties in closely with the next one, but also tie in closely with things that happened in the previous episodes.

My questions are:

1. How do television writers think of enough material that would last for seasons upon seasons without giving too much info away that could end the entire season let alone give just a bit of info so it won't end the entire episode..which ultimately leads us to the next one.

2. How do television writers make everything connect so well? It's almost as if they write all the episodes backwards from the last episode to the first one. Because everything connects so well.

I hope this makes sense?! can anyone help me out?

1. The same way someone can write a dozen books in a series or make a movie with 3 sequels.

2. Actually yeah they sort of do that sometimes. Lots of things aren't filmed in order and they usually have the actual plot and story fairly well thought out before any production begins