You need diet and exercise to lose weight. You want to start out with a very easy warm up ride for the first 10 min. I increase the resistance a little about every 3 min to get warmed up. After the warm up you want to pedal at 70-90 rpm's with just enough resistance to get your breathing to the point where you can still talk but not sing. If you need to catch your breath or your legs start to hurt drop back on the resistance and pedal at 70 rpm's as you recover increase the speed and resistance. You should be breathing hard and sweating to see good results. I usually start sweating after 15 min or so and ride about 40-45 min at a time. You may want to go only 20 min at first untill your butt gets use to the saddle.
Don't expect to see any big results in the first few weeks unless you reduced your calories. Stay away from soda, fast food and junk food they contain a lot of calories. You need to get you bodys cardio system to the point where you are burning a lot of calories. It takes tine to do that.