Help!!!Question about filing income tax...I'm a green cardholder.?

You are required to file an income tax return for any year for which you had at least a certain amount of income, even if you were not in the U.S. for any days and only worked for one day out of the year. In the unlikely event that you are not required to file, but decide to file anyway, the government usually sends you money, and never charges you money. There is never a downside to filing. Either (a) you are required to file, (b) filing will not result in you paying the government any money, and will probably result in you receiving money, or (c) both. There is no situation in which filing unnecessarily will result in you paying the government money.