Your younger sister is doing her taxes. She's used an accountant to do her taxes for the past few years, but this year she's going to do it herself. She asks you whether she should use Form 1040 or Form 1040-EZ. You tell her:
If you make less than a hundred thousand dollars, you should fill out form 1040-EZ.
make (an amount of money)
To "make ___" means that you get paid that much for your job. If you say:
I make fifty thousand.
It means that you get paid 50,000 dollars, euros, yen, or whatever form of money is used in your country.
You can tell what the time period is for this amount using "per ___":
I make fifty thousand dollars per year.
A more casual way of saying the same idea is "make ___ a ___":
She only makes ten bucks an hour.
a (hundred/thousand/million)
"A hundred" means "100".
This number can also be said as "one hundred". But saying "a hundred" is more casual and less exact. "one hundred" means exactly 100, but "a hundred" sounds like it might be a little more or a little less than precisely 100.
you should (do something)
Telling someone "you should ___" is a way of giving advice. You use the word "should" when you don't think the person will mind you giving them advice. For example, in this case your sister doesn't know which form to use, so she's happy to hear your advice.
If you want to give someone advice that they're not expecting and might not like, you can use an expression like this:
If you make less than a hundred thousand dollars, you're supposed to fill out form 1040-EZ.
fill out (a form)
A "form" is a document with blank lines or boxes that you write information into. 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 blanks or boxes.