Generally the phrase
"you get the idea" is then followed by several more
sentences in which the speaking person further
extrapolates and
elaborates on said
idea, causing the individual listening to either feel
stupid because he still doesn't get it, or else causing the listening individual to verbally or nonverbally (through
body language) indicate to the speaker to please stop yammering on about it because he is fully aware that "you get the idea" means that he should already understand the situation enough, and that he does, and they really should get going because that very large creature made up of whatever it was the speaker had been nonchalantly elaborating about is now
breaking down the door and will soon eat them if they don't get out of there and continue on with the
plot.
The phrase "you get the idea" is often used in poorly written B-rated movies. It's also often used in Everything2, which may be a giant secret of the universe connecting the one with the other, but you get the idea...