No worries Bo. Glad to help out someone learn, after all I need that kind of help from time to time as well.
Let's see, how to explain how Venom is...
Well, the first thing is, you know that Peter Parker works at the Daily Bugle right? OK, there's another reporter there named Eddie Brock who gets a bit jealous and angry that Peter always gets the scoop before he does.
Now, I don't know how it'll get treated in the movie, nor exactly how it is in the comics books, but here's how it generally goes.
There are these creatures known as "symbiots", living sentient beings that are basically masses of black ooze. They attach to a host being and take it over, turning them into lethal or more ruthless and agressive beings. The symbiot first bonded with Peter, and then it adopted the form of his classic Spider-Man uniform because Peter willed it at the moment. Sort of a quick-change ability, making for an instant uniform without needing to actually change from his normal clothes to any spare uniform he'd need at that moment.
This is what we refer to as "Black Suit Spider-Man".
After Peter started to study what the symbiot was and what it was doing to him, he doesn't like what's happening to him... And eventually rejects the suit, though the suit doesn't want to let go... Until he finds out that loud sounds like being directly next to tolling church bells or rocket engines hurts, and even dislodges the symbiot from its host.
The symbiot loses its hold on Peter... But then Eddie Brock finds it, which holds the knowledge of Peter's secret identity, and the anger inside him makes it the perfect host. When the symbiot merges with Eddie, it creates a new being known as Venom. Not only does Venom have the knowledge of who Spider-Man is, but it also has all of the original's abilities.
And if that weren't enough, there are three other symbiot characters, but it's not important at this time... Wouldn't want to muddle things for you.
LMK if you want to know the 4th villian, and I'll PM you Bo... If your PM box's got some space that is.