Went to purchase a pre-owned car at a Hyundai Dealership. There was none. Was shown a new car. The deal was processed, asked to sign w/o explanation

Please don;t judge. Went to Dealership to purchase a pre-owned car; There was none. Was shown a new one; I said I liked it but knew I couldn't afford it. I am an 83-years-old living on SS. Said to Salesperson "make sure I am told what the monthly payment will be so I know whether I could afford it. Her reply was "Oh, the manager will explain." I was shown to the manager's office where there was some sort of computerized table with pages spinning around. My attention was focused on these pages - not realizing they were the contract. I was told by the Manager - sign here, with table spinning to the next. Absolutely no explanation was given as to monthly payments for the car or the insurance. When I got home it was then I knew what had happened to me. During this time of signing the thought of the Manager discussing terms of sale to me, went completely out of my head. I have not slept a wink since 09/02/17. Needless to say, I did not know that I could have returned the car