New to weight loss plan

you should absolutely lift weights. you have muscle on your body and, no matter what, you always will. muscle uses a lot of energy (i.e. calories), so the more muscle you have, the more calories you burn, the more fat you lose. also, if you don't lift, you could lose muscle instead of fat, which would make you soft or, if you cut to a low enough body fat percent, skeletal. if you prefer the softer look, then don't lift weights. if you want to look "toned", lift weights. either way, 30 minutes of cardio is great! although i would probably stick more with the stairmaster and do interval training because it tears up your lungs more and really works your legs/butt. the vast majority of the time, you should be dripping when you're done on the machine, although feel free to have easier recovery days.
if you decide to lift weights, you should do a lot of compound moves with as much weight as you can with good form (ask for help from somebody at the gym who knows what they're doing, not the guy with a huge upper body and chicken legs. especially don't ask him for help with squats.). do bench presses (bonus: growth of pectoral muscle can make your boobs look bigger and perkier), squats and lunges (bonus: great *kitten*), overhead presses (bonus: increasing the size of your shoulders and lats will create a taper which makes your waist look smaller), deadlifts (bonus: you can usually deadlift a lot more than any other lifts and will look super impressive), and rows (bonus: again, increasing upper back size makes waist look smaller, also can help with your posture, and good posture makes your chest look bigger and belly look flatter).

ETA: you should aim for between five sets of five to three sets of eight. when all of the reps are easy, increase the weight.