If you have a checking/savings account, you already have a credit score. If youre over 18 and have those accounts and have been told that you have "0" credit score, the creditor is just being a douche - ultimately trying to justify selling you a higher APR. Zero [not 0 credit score] credit means that you just don't have much of a credit "history" - which will matter more when taking out a mortgage and/or car loan in terms of rates. As for your grad plus, as long as you don't have anything derogatory, the government pretty much guarantees it. Note that if you go to an affordable state school, you may not even need anything above stafford loans.
As for building up your credit. Go for it. You will need it sooner or later. However, I would take anything someone on SDN says with a grain of salt. A debit card will not build your credit - its linked to your checkings (no credit involved). A debit card will pull cash from your account immediately while a credit card provides a revolving line of credit which allows you to make monthly payments. How much revolving/static credit open:used, longevity of credit accounts, etc. will affect your score. I agree, you just need to use a small amount and pay it off every month.
