Beginning to exercise

I'm 19 and going to start exercising and I have a gym membership. A personal trainer at my gym is too much money so that's not an option. I was 120 pounds but I gained 13 pounds I'm a year so now I'm 133 pounds. I'd love to get back down to my original weight. However, I am very weak all around. I know I need to do strength training to build muscle and cardio to lose weight but I don't know what machines or exercises to do. I also know I have to eat healthy. What exercises/machines did you use when you first started going to the gym?