I m just a freshmen so there is no way I can apply for study abroad scholarship/academic opportunities…
however, if I am apply for Green card, and if I leave the country for education purpose such as this, will this negatively affect me??
When you have your green card, you can travel outside the US for less than a year. However, some immigration lawyers recommend that you should plan to return within 6 months just to be on the safe side. If you would need to be outside the US for more than a year, you need to get a Reentry Permit before you leave. http://www.uscis.gov/sites/default/files/USCIS/Resources/B5en.pdf
Travelling on advance parole (while you are applying for your GC) can be tricky. It is doable and as long as you have your paperwork in order, the riskiest time as always is re entering the USA. You will get special attention. Are you independently getting your GC? How old are you? At this point worrying about the travel on the GC is premature.
My mom will get green card soon and through her I will apply for GC. I just turned 20
Well, I think to get a GC as a dependant it must be applied for before you turn 21. You don’t really have time on your side if your mum doesn’t even have her own GC, so this is all a bit moot until you she has filed your GC application. Once the GC application is filed your age freezes as long as it is before you turn 21. The once you have your application in progress, travel is on an advance parole and again you would want to take advice as to the risk that might create. GCs sometimes take years to acquire.
paul2752 - Are you already included in your mom’s paperwork? If not, can you be added to it? Talk with her immigration lawyer and find out your options.