Bench Pressing? How to begin?

3 X 10 means three sets of 10 repetitions each. At your weight I would begin with 100 pound and that is all. See if you can do 3 X 6 at first and work up to 3 X 10. Add about 5 pounds to this weight every week until you reach your body weight in many months. Do not worry about the weight gain. Muscle weighs far more than fat and your routine is building up muscle each day. Increase your jogging and running to about 3-4 miles at a time, and I would not hesitate to do this twice each day since you are young and quite physically fit. By September you will be amazed at what you will be able to accomplish if you stick with it everyday. There is no need to take any days off at your age as long as you make certain you are getting 10 hours sleep each night and with your intensity of workout that should not be a problem. Have meals heavy with protein and no sugar, no coke, no diet drinks and drink water, water, water. In fact "Google" water and weight loss and you will see what I mean. Water only...no other drinks. You should be drinking a minimum of 80 ounces of water each day! Keep it up and regardless of your reason why you are doing this, you will be a whole new person by Labor Day...and that will seem like just a day or two away. Jogging and walking is the greatest thing I have ever done and I am going 4 miles in the heat of the day at an age of over 50! So think of what you can do at 17....WOW!