1. HOW LONG US CITIZEN CAN STAY OUTSIDE THE US,,,,

2. HOW DO I FILE ( GREEN CARD ) MY SISTER.

Hahahaha... if you are a US citizen, you have total freedom to stay outside of the US as long as you want.

As for filing for green card, talk to a lawyer.

THANK YOU NEP-AME. ANYBODY KNOW HOW TO FILE GC FOR MY SISTER.. PLS..

Stopthewar, check this link. You will get the information you need.

http://1.usa.gov/qRWUb            for parents

http://1.usa.gov/4d11e4            for siblings

Sparty

 You can stay outside USA as long as you want. Just get the visa and you are all set.  Form I-130 is needed to fill for siblings and Form I-485 for adjustment  for the status if already in US.

Unitednepali

thak you for your information. My sister is in nepal, so you mean i i have to fill up i-30 form only or other form too... pls can u tell me.

 @stopthewar: No offense bro but are you gonna ask how to fill up the form too. Do some research by yourself too bud. The link above tells you everything. Kasta kasta manche U.S. Citizen huncha yaar. 

swastikbhai,,,

thank you for your comment but just i want to share other people advise. i don,t thik there is anywrong. anyway thankx.

 The form is called I-130 form. Once you file and form and that petition gets approved, they'll put her case to a waiting period until the visas become available in that category. Usually, the wait is 10+ years for brothers/sisters. Hope that helps. Read the I-130 form instruction in the www.uscis.gov webiste.

 correction - Once you file the form....

Thank you nepali thito23