“You have to fill out a bunch of paperwork.”

You moved to the U.S. a few years ago from another country. You had to apply to get a green card, and it was difficult. Now you're talking to a coworker whose friend is also applying for a permanent residence card. You're describing how difficult it is. You say:

You have to fill out a bunch of paperwork.

You

The word "you" doesn't always mean the person who you're directly speaking with. Sometimes it means 
"people in general" or "anyone". In the example sentence above, the speaker means that anyone who applies for a green card has to fill out a lot of paperwork.

Here are some other examples of "you" used in a general way:

You need a solid foundation in basic math and science.

You can't beat face-to-face communication, you know?

fill out (a form)

A "form" is a document with blank lines or boxes that you write informationinto. Forms were originally printed on paper, but now forms are common on the Internet. You can see them whenever you sign up for a new website and have to enter your name, email address, and other information.

To "fill out" a form means to write answers into the blank lines or boxes.

Here are some words that you can use after "fill out":

fill out an application

fill out paperwork

fill out a registration form

fill out a survey

a bunch of (something)

"A bunch" means "a lot" or "many".

It's a casual expression and can sound kind of childlike.