You build your credit score by paying all your bills promptly and getting rid of any outstanding debts as fast as possible. If you already have a credit card, use it and PAY IT OFF PROMPTLY. A great book full of basic advice on this whole subject is
here.
Real estate is a great investment right now because so many places are going for a song after foreclosure. Seriously, you can buy some foreclosed properties in nice areas for the price of a new motorcycle.
If I were you I would start putting small amounts away in some sort of well-rated mutual fund, either towards retirement or for seed money for other investments like real estate.