(Please move this post if it is in the wrong place...)
Hi everybody
I am a 15 year old boy
I really need to enlarge my shoulders and strenghten my biceps and triceps
All without any machines or weights
Can you advice me some exercises and maybe do me a plan (like every day 3*8 pushups or something like that)
Thanks in advance

You don't have access to any machines or weights? Your school doesn't have a weight room? I'd be very surprised at that. Regardless, IMO the Navy Seal program is the best bodyweight workout you can do. Here's the link

Oh, and don't forget to eat big! You don't grow if you don't eat enough. Plain and simple.