A crash course in changing the world.
The experience that I have done is saving money that my parents gave me for buying lunch. My parents give me money every week for lunch and my maid will make the breakfast. Sometimes, my maid will make a big amount of breakfast and I can't finish it, so I will continue eating it on lunch time. That means that I don't need to buy any lunch and I can save my lunch money. I have two saving box, one is for coins money and one is for the leftover lunch money. For the coin saving box, I can't use it until it's the saving box is full. Then, for the leftover lunch money, I can't use any of it, unless it's emergency condition, because the money for the time in future, I'm not sure when is it.
There is also one other experience that I had done, it's about exchange/trade something with my friend. My friend in my old school needs help with his homework. He asked me to teach him the homework that he don't understand and he said that he will bring food for me as an exchange. I think that this is also called exchange/trade, because I trade teaching my friend homework with the food that he brought for me.