There's no secret

It does not matter how you choose to do it, any physical activity is good activity. As long as you get out there and do it you're making progress.
There is also no major number of reps or sets or amount of weight that you need to be doing. Everyone is different and everyone works at a different pace. You just need to figure up what works best for your body and go at your own pace. There is not one secret way to get the best results. A certain thing may work great for me but not for you or visa versa. It takes time to figure out what works best for you and what you enjoy doing. Don't think that right off the bat you are going to find the perfect way to slim down and get in shape. It definitely took me a long time. I originally thought that I just needed to run a lot because I needed to loose my fat and I didn't want to get bulky. (Typical thought process of most females). It wasn't until just recently that I've learned what routine and foods work best for me.
So don't give up! It takes time. Results won't happen over night and there is no perfect routine. So go try different routines, different foods, and stay focused on your goals! Mix it up a little too so you don't get bored.

Here is a good chest workout that I did today. It's pretty short so I added some ab exercise and a couple back exercises because I felt like I need a good stretch.

Everything was 4 sets of 10
Cable cross overs
Barbell incline bench
Dumbbell bench press
Pec dec flies
Push-ups 4 sets of as many as you can

It is a short workout but its still something and its progress!
Do as many reps/sets as you feel. Switch it up 4 sets of 10 or 3 sets of 15 or whatever you'd like, just do it!