Please put this is simple terms, I dont know what Hiit or whatever that other stuff you guys say is.

Will lifting weights (dumbbells) or buying a speedbag help?

The most important thing is diet. You can lift weights until the cows come home, but it isn't going to get rid of your manboobs alone. You need to eat a healthy, balanced diet. Lean white meats, oatmeal, whole wheat bread, cottage cheese, fish, that sort of thing. Cut out soda pop as well - drinking 3 cans of cola per day, for one week, equals approximately 3150 calories! That's more than a day's allotment of calories for osme people.

Once you've fixed your diet, then you can worry about the weights. Try to have both weight lifting (dumbbells are okay) and cardio (running, treadmill, etc.), and you'll be on the way to being a thinner you.

HIIT is high intensity interval training. simply after a proper warmup, you go all out for roughly 30 seconds, let up to allow for recovery then go all out again. you go no more than 10-15 minutes.

if done properly, its very hard. work your way into it.