I just got my green card and know I have to fill my tax return next year. I am a foreign citizen, but legal US resident. I received my old age pension from abroad. They put it in a bank account there, and I use my debit card to get my money here, in the U.S. What kind of form should I use to fill my tax return. Should I need to know something else? Thank you very much for your attention to this message.

You will file a form 1040.
You will report your pension on line 16a and b as income.
If any tax is being withheld on your pension in your home country you may be entitled to take a credit for that tax.
Depending on what country you come from and from what employment gave rise to this pension you may be entitled
To treaty benefits and either the US or your home country may be required to allow you a credit against tax paid to that other state.

Thank you very much for your answer