What is an email marketing funnel really?

What is an email marketing funnel really?

OK now call me dumb or something but I don't quite understand what an email funnel really is.

I have been invited by so many people to join in these so called amazing email funnels. I have been told I can get like hundreds of fresh leads a day. Ok so it sounds great so far.

Now this is what I don't get. From what I can understand from the outside I am required to give my email address and details over when I sign up right?

Then from then on every single person that signs up to the website after me gets added to my funnel so I have their details.

So that would also imply that MY email address and details have been shared with every single person on that website too.

Then I can email all those people with offers?

I'm sorry but why am I the only person that looks at this and says it completely sucks?