What are some exercises a 13 year old can do daily to get real buff without a gy!

Push ups with your feet up on a chair. Sit ups. Use some heavy cans of food of equal weight and you can do arm curls. At 13 your metabolism is so high that it will be very hard to gain lots of mass but exercise that you do now will help pay benefits in the future. I lifted weights at your age but sorry to say I never gained any mass till I turned 30. Now I can pack on muscles easily.
Right now a good diet and plenty of sleep will help you and when your metabolism changes it will be easier in the future for you to make gains in mass. Don't give up staying healthy Good Luck! Stay away from cigarettes and drugs and alcohol and you will be one step up on a lot of people when you get older.

been there done that

Jog a few miles a day right after school make sure you drink alot of water while doing so when you get home do pushups till you can feel a small burning and if you can still do more go for it it means its working then go to sit ups if you dont feel it working then you might want to switch up how your doing them and when you done and go eat dinner or lunch or whatever drink milk and dont have to many fatty foods after or during meals, this is pretty much the best way without a gym, or get a wieght set.

First, you might want to think about starting to exercise at such a young age. Studies have shown that if you start working out at a young age, it can cause you to stop growing earlier, and grow less in the meantime. Push-ups are the easiest exercise to do, as long as you have a small area of open space. Also doing planks (laying down with your back flat to the ground and holding your legs a few inches above the ground) is good for abdominal muscles. Run regularly to keep your heart in good shape. Try doing Parkour, it's great for an overall workout and improves your flexibility and your stamina.