I started working out at the gym today. I'm 25 year old, 173cm, 78kg. I'm overweight and I need to lose weight. I'm doing one hour of cardio and I lift weights as well. In the gym there is a boxing bag and i feel I want to try boxing and maybe reduce some of the cardio for the boxing or alternating. So I will see later how I will tune this. But I never tried boxing before and I really have no idea what to do with the boxing bag. Can you suggest some good exercises that build strength and lose fat with boxing? If you can post some good videos for that, it would be great. Also if you have some advise for my routine at the gym with the boxing and other stuff I'm doing, that also would even better!
Anyone can box. I started when I was 18. My first months in the gym would probably be laughed at by most including myself. You have to start somewhere.
You aren't going to kill yourself punching a bag. You also aren't going to get a magical fat loss explosion.
If you want to punch the bag I would start with 1 minute on 1 minute off until you can work up to 4 minutes on and 1 minute off. You need to have wrist wraps on and some type of glove (heavier gloves = more workout). Simply circle bag with your off foot in front and throw jab/punch combinations. This is what any new boxer should do. You should not be lunging into the bag but a simple 6"-12" step on punch is OK. The top of your gloves should reflex right back to eye level. Probably the only harm you can do to yourself is standing too far from bag and overextending your elbows/shoulders. Bags don't punch back.
However I would not expect much if any fat loss from doing this. You might get more tone in your back and shoulders but not fat loss. To even add onto this if you are taking away running or useful cardio and doing this instead then you are working in the wrong direction. That stuff will contribute to fat loss.
Most people want to do boxing routines because they want to look like boxers. I got people all the time to try to get me to teach them the "boxer routine" so they could be cut. Bag work is probably 20% of the equation. And the heavy bag isn't even half that. The uppercut bag works your core and back far more than a normal heavy bag and has a much greater effect on overall physique.
But really what makes boxers cut and defined are the less glamorous things. We run a lot. Both long distance and sprint training. I would run 5 miles at least twice a week and at least twice I would do 20-30 sprints (50 yardsish). Then there is the jumping rope at 4 x 20-30 minutes a week. In my opinion there isn't a better exercise in the world that is geared towards shedding fat and low impact (relatively) as jumping rope - two feet down, two feet up.
Then there are the situps, shadow boxing, weighted movements and other things. Please please do not equate losing fat with punching a bag.
A general rule I live by with cardio and I know this is a vast generalization is - if you are doing something because it is easier it probably won't be as effective. So in your case you are thinking I want to hit the bag for 30 mins vs running for 30 mins. Well no duh I would too. But I also would know that really there is nothing like running to lose fat/weight (I am talking about training here not diet).