Well you won't be able to lose 20 pounds as soon as you want, however, a loss of about 1 pound per week is a reasonable target. This will, however, require some dedication on your part by keeping track of the amount of calories you consume and the amount of calories you are burning. Bear in mind, that you are probably using about 2000 calories per day without exercise. So, give yourself a 500 calorie deficit each day, and you will lose 1 pound per week (3500 calories is approximately 1 pound of body fat).
You want to be eating less, but more often, so, ideally 5 or more meals per day. Each meal would ideally consist of about 300 calories - so for example for one you could have a banana and a cereal bar etc.
Now, for exercise, I would suggest some HIIT (High Intensity Interval Training), as well as some weight lifting. HIIT involves taking any type of exercise that is sustained i.e. running, cycling, ergoing etc. What you do is begin by warming up for 5-10 minutes. Then, for the main part of your workout, you could do something on the lines of sprint for 30 seconds rest for 20 etc. I'm sure that the guys in the HIIT forum could tell you more.
Now, for muscle building, it would be ideal if you had access to a gym which you could visit about 3 times a week. There, you would perform something like 4 sets of 8 reps on various weight lifting exercises.
If you don't have access to a gym, then a good investment would be some dumbells. If, however, you are not feeling like investing in any, then simple body weight exercises performed every day or two should be ideal. Press ups, sit ups, planks etc.
