watch this guys videos. His main goal in the vids are to help people lose fat and put on muscle.
Dont just start watching random videos. Start from the begining.
One thing to rememeber is, doing the same workout over and over will produce less and less results. You must keep changing your work out. For example, if you are just doing situps, then you might lose a little fat around your abdominals, and your abs might become more muscular, but eventually they will adapt and your progress will slow down then eventually stop. By changing the workout, you are using the muscles in different ways, and you will feel more of a burn. The more you do of a workout, the less burn you will get because your muscles adapt to the burn.
Follow this guys tips and you are sure to see great results.