Net pay is the take-home pay after taxes and deductions, and gross pay is the total amount earned before taxes and deductions.
"Gross" means the total amount of your wages. What you "net" or gather into your bank account.
Let's use an example, and for the sake of state tax numbers, let's say you live in Minnesota. If you had a job where your total amount earned in a week (gross pay) was $1,000, and you got a weekly paycheck--assuming you are single and claiming no special tax deductions:
Federal income tax would be about $125
Social Security withholding about $60
Medicare withholding about $15
State tax withholding about $60
... So, not counting any other deductions you might include (such as your portion of health or dental insurance premiums, etc), with a gross pay of $1,000 your net pay would be about $740. That's what would get deposited to your bank account or given to you in check form.