Us immigration

Your question is a little confusing. Are you trying to find out what form your parents need to file to come to the USA?

I am a Naturalized US Citizen and I filed for my parents.

First your sister, not your parents, must file an I-130 Petition for Alien Relative ($190). She will send whatever is requested on that form.

After the I-130 is approved, USCIS will send the original visa petition to the Department of State National Visa Center, where they process all approved immigrant petitions that need consular actions.

The National Visa Center will then send your parents a list of documentation they will need:
Application for Immigration Visa and Alien Registration Form DS-230 Part I
The Affidavit of support fee bill
Information about Agent of Choice letter (to ask if they wish to name a representative (i.e., your sister) to act on their behalf or if your parens choose to take it from there and work with the Visa center themselves to provide any remaining paperwork required).

Your sister will need her birth certificate and that of your parents as well as your parent marriage certificate to show that they are truly related, etc...which your sister will need to have translated to English at a certified translator (I had them translated at the Consulate here in the USA).

There will also be a request for medical exams to be done......... It's a long process