Ill start from how it happened...
I am a 13 year old boy. Today, I ate two plates of spaghetti...and right after that, i went poop. I looked at it and saw reddish things. I thought it was blood...I then asked my older brother what it was...he said to wait until it happened again...my other bro said it was just the spaghetti...
Can any of you help me, please?

No need to worry. The odds of it just being particles of undigested foods are very great. When you eat a large meal, such as 2 plates of spagetti(lol), the digestive system has a hard time breaking down all the food so some of it doesn't digest and you just pass it. I don't think you have anything to worry about but next time you have a bowel movement just take a look and you will see everything is fine. Don't worry!