Hi Maria You are wise to seek help before talking to a foundation contractor; not becuase they will try to deceive you...most are honest. But it sure helps to know what they are talking about!
I'd recommend you get a book from your library or home improvement center to help you understand the basics. Time-Life has an excellent book on foundations with some of the best pictures I have seen. "Contracting your new Home" is a book published about 10 years ago by, I believe, Strobel, who has a whole chapter devoted to subcontracting the excavation, footings and foundation walls of a house. Read, read, read. Its not difficult to understand, but it will take some time.